Roll No : Name of School : Time - MM- 251

Date : Name of Assessment :

Subject :
Class :

1 A proton strikes another proton at rest. Assume impact-parameter to be zero, 2

i.e. head-on collsion. How close will the incident proton go to other proton?
2 Find the ionization energy and ionization potential of ground state electron in 2
hydrogen atom.
3 What is the angular momentum of an electron in Bohr’s hydrogen atom 2
whose energy is –3.4 eV?
4 What is the difference between Rutherford and Bohr’s model? 2

5 Draw a labelled diagram of Geiger and Marsden experiment on α-particle 2

scattering. Explain how does it help to find the size of a nucleus.
6 State Bohr’s postulate of hydrogen atom which successfully explains the 2
emission lines in the spectrum of hydrogen atom.
Use Rydberg formula to determine the wavelength of Ha line.
[Given: Rydberg constant R = 1.09 × 107 m–1]
7 Using Rutherford model of the atom, derive the expression for the total energy 2
of the electron in hydrogen atom. What is the significance of total negative
energy possessed by the electron?
8 Find the relation between the three wavelengths λ1, λ2 and λ3 from the energy 2
level diagram shown below.
As ECA = ECB + EBA

9 Define ionization energy. How would the ionization energy change when 2
electron in a hydrogen atom is replaced by a particle of mass 200 times that of
the electron but having the same charge?
10An electron during its transition from second excited state to ground state 2
emits the radiation of wavelength λ. Answer the following:
(a) In which series of transition this emission lies?
(b) Name the region of em wave spectrum.
11An atom absorbs a photon of wavelength λ and then re-emits the energy in 2
two steps. If one emitted wavelength is 3 λ, what will be the other
wavelength?
12Determine the ratio of distance of closest approach of a proton and an alpha 2
particle incident on a thin gold foil, if they have same kinetic energy.
13Define the distance of closest approach. An a-particle of kinetic energy ‘K’ is 2
bombarded on a thin gold foil. The distance of the closest approach is ‘r’.
What will be the distance of closest approach for an a-particle of double the
kinetic energy?
14State Bohr’s quantization condition of angular momentum. Calculate the 2
shortest wavelength of the Bracket series and state to which part of the
electromagnetic spectrum does it belong.
15In the study of Geiger-Marsden experiment on scattering of a-particles by a 3
thin foil of gold, draw the trajectory of a-particles in the coulomb field of target
nucleus. Explain briefly how one gets the information on the size of the
nucleus from this study.
From the relation R = R0 A1/3, where R0 is constant and A is the mass number
of the nucleus, show that nuclear matter density is independent of A.
16In an experiment on α-particle scattering by a thin foil of gold, draw a plot 3
showing the number of particles scattered versus the scattering angle θ. Why
is it that a very small fraction of the particles are scattered at θ > 90°?
Write two important conclusions that can be drawn regarding the structure of
the atom from the study of this experiment.
17Consider energy level diagram of a hydrogen atom. How will the kinetic energy 3
and potential energy of electron vary if the electron moves from a lower level
to a higher level?
18Using Bohr’s postulates for hydrogen atom, show that the total energy (E) of 3
the electron in the stationary states can be expressed as the sum of kinetic
energy (K) and potential energy (U), where K = – U. Hence deduce the
expression for the total energy in the nth energy level of hydrogen atom.
19Using Bohr’s postulates, obtain the expression for the total energy of the 3
electron in the stationary states of the hydrogen atom. Hence draw the energy
level diagram showing how the line spectra corresponding to Balmer series
occur due to transition between energy levels.
20Using the postulates of Bohr’s model of hydrogen atom, obtain an expression 3
for the frequency of radiation emitted when the atom makes a transition from
the higher energy state with quantum number ni to the lower energy state with
quantum number nf (nf < ni).
21(a) Using Bohr’s second postulate of quantization of orbital angular 3
momentum show that the circumference of the electronic in the nth orbital
state in hydrogen atom is n times the de Broglie wavelength associated with
it.
(b) The electron in hydrogen atom is initially in the third excited state. What is
the maximum number of spectral lines which can be emitted when it finally
moves to the ground state?
22 (a) Using postulates of Bohr’s theory of hydrogen atom, show that 3
(i) the radii of orbits increases as n2, and
(ii) the total energy of the electron increases as 1/n2, where n is the principal
quantum number of the atom.
(b) Calculate the wavelength of Hα line in Balmer series of hydrogen atom,
given Rydberg’s constant R = 1.0947 × 107 m–1.
23Using Bohr’s postulates, obtain the expressions for (i) kinetic energy and (ii) 3
potential energy of the electron in stationary state of hydrogen atom.
Draw the energy level diagram showing how the transitions between energy
levels result in the appearance of Lyman series.
24(a) The energy levels of a hypothetical hydrogen-like atom are shown in the 3
figure. Find out the transition, from the ones shown in the figure, which will
result in the emission of a photon of wavelength 275 nm.

(b) Which of these transitions corresponds to the emission of radiation of (i)

maximum and (ii) minimum wavelength?
25If the energy of an electron in H-atom is Then using above 3

expression show that (a) an electron cannot have energy of – 2V. (b) spacing
between energy levels decreases as n increases.
26 Write shortcomings of Rutherford atomic model. Explain how these were 3
overcome by the postulates of Bohr’s atomic model.
27 Using Bohr’s postulates, derive the expression for the orbital period of the 3
electron moving in the nth orbit of hydrogen atom.
28(a) State Bohr’s postulate to define stable orbits in hydrogen atom. How does 3
de Broglie’s hypothesis explain the stability of these orbits?
(b) A hydrogen atom initially in the ground state absorbs a photon which
excites it to the n = 4 level. Estimate the frequency of the photon.
29(a) How did de Broglie hypothesis provide an explanation for Bohr’s second 3
postulate for quantisation of orbital angular momentum of the orbiting
electron in hydrogen atom? Discuss.
(b) Identify the transition of electron in Bohr model which gives rise to (i) the
maximum, and (ii) the minimum wavelength in Balmer series of hydrogen
spectrum.
30Using Rydberg formula, calculate the wavelengths of the spectral lines of the 5
first member of the Lyman series and of the Balmer series.
31Using Bohr’s postulates, derive the expression for the frequency of radiation 5
emitted when electron in hydrogen atom undergoes transition from higher
energy state (quantum number ni) to the lower state (nf).
 When electron in hydrogen atom jumps from energy state ni = 4 to nf = 3, 2, 1,
identify the spectral series to which the emission lines belong.
–11
32The radius of innermost electron orbit of a hydrogen atom is 5.3 × 10 m. 4
What is the radius of orbit in the second excited state?
33A single electron orbits around a stationary nucleus of charge +Ze, where Z is 4
a constant and e is the magnitude of electronic charge. It requires 47.2 eV to
excite the electron from the second to the third Bohr orbit. Find the value of Z.
34Determine the maximum wavelength that hydrogen in its ground state can 4
absorb. What would be the next smaller wavelength that would work?
35Find the ratio of minimum to maximum wavelength of radiation emitted by an 4
electron in the ground state of Bohr’s hydrogen atom.
36The second member of the Lyman series in hydrogen spectrum has 4
wavelength 5400 Å. Find the wavelength of the first member.
37Determine the ratio of distance of closest approach of a proton and an alpha 4
particle, incident on a thin gold foil, if they are accelerated through same
potential difference (V).
38 If λ1 and λ2 are the wavelengths of the first member of Lyman and Paschen 4
series respectively, then determine the ratio λ1/λ2.
39A 12.5 eV electron beam is used to bombard gaseous hydrogen at room 4
temperature. Upto which energy level the hydrogen atoms would be excited?
Calculate the wavelengths of the first member of Lyman and first member of
Balmer series.
40The electron in a given Bohr’s orbit has a total energy of – 1.5 eV. Calculate its 4
(i) kinetic energy, (ii) potential energy and (iii) wavelength of radiation emitted,
when this electron makes a transition to the ground state.
[Given: Energy in the ground state = – 13.6 eV and Rydberg’s constant = 1.09 ×
107 m–1]
41 The ground state energy of hydrogen atom is –13.6 eV. 4
(i) What is the potential energy of an electron in the 3rd excited state?
(ii) If the electron jumps to the ground state from the 3rd excited state,
calculate the wavelength of the photon emitted.
42The ground state energy of hydrogen atom is –13.6 eV. If an electron makes a 4
transition from an energy level –0.85 eV to –3.4 eV, calculate the wavelength
of the spectral line emitted. To which series of hydrogen spectrum does this
wavelength belong?
43The energy levels of an element are given below : 4
 Identify, using necessary calculations, the transition, which corresponds to the
emission of a spectral line of wavelength 482 nm.
44 The ground state energy of hydrogen atom is – 13.6 eV. 4
(i) What is the kinetic energy of an electron in the 2nd excited state?
(ii) If the electron jumps to the ground state from the 2nd excited state,
calculate the wavelength of the spectral line emitted.
45Using Rydberg’s formula, calculate the longest wavelengths belonging to 4
Lyman and Balmer series. In which region of hydrogen spectrum do these
transitions lie? [Given R = 1.1 × 107 m–1]
46A 12.9 eV beam of electrons is used to bombard gaseous hydrogen at room 4
temperature. Up to which energy level the hydrogen atoms would be excited?
Calculate the wavelength of the first member of Paschen series and first
member of Balmer series.
47What should be minimum energy required by ground state electron in 4
hydrogen atom so that three lines are obtained in its emission spectrum?
48(a) In a Geiger-Marsden experiment, find the distance of closest approach to 4
the gold nucleus (mass no. = 79) of a 7.7 MeV α-particle before it comes
momentarily to rest and reverses its direction. Why is it different from actual
radius of gold nucleus?
(b) Plot a graph between number of scattered a-particles detected in gold foil
experiment and angle of scattering. What is the main assumption in plotting
this graph?
49 The radius of innermost electron orbit of a hydrogen atom is 5.3 × 10–11 m. 4
What is its radius in n = 3 orbit?
50 Find out the wavelength of the electron orbiting in the ground state of 4
hydrogen atom.
51Calculate the wavelength associated with the electron revolving in the first 4
excited state in hydrogen atom. The ground state energy of the hydrogen
atom is –13.6 eV.
52 If λ1 and λ2 are the wavelengths of the first member of Lyman and Paschen 4
series respectively, thendetermine the ratio λ1/λ2.
53The short wavelength limit for the Lyman series of the hydrogen spectrum is 4
913.4 Å. Calculate the short wavelength limit for Balmer series of the
hydrogen spectrum.
54 ? 4

55In 1912, Neils Bohr studied the spectrum of hydrogen in Rutherford Laboratory 5
and concluded that the limitations of Rutherford’s atomic model cannot be
explained using classical mechanics and electromagnetism. He proposed the
first quantum model of the atom by combining concepts of classical and
quantum mechanics. He explained the structure of atom and its stability.
 (i) In terms of Bohr radius r0, what is the radius of second Bohr orbit of
hydrogen atom ?
(a) 4r0
(b) 8r0
(c) √2 r0
(d) 2r0
(ii) The kinetic energy of electron in the first excited state is 3.4 eV calculate.
Its potential energy in this state is
(a) – 3.4 eV
(b) 6.8 eV
(c) – 6.8 eV
(d) 3.4 eV
(iii) The ionisation energy of electron in a hydrogen atom is 13.6 eV. What is
the energy required to remove electron from the second excited state is
(a) – 13.6 eV
(b) 1.51 eV
(c) – 1.51 eV
(d) – 3.4 eV
(iv) The largest wavelength in the UV region of hydrogen spectrum is 122 nm.
What is the smallest wavelength in the infrared region of the hydrogen
spectrum ?
(a) 802 nm
(b) 823 nm
(c) 1882 nm
(d) 1648 nm
Or
(iv) In Rutherford’s atomic model, the electrons
(a) experience no force in the innermost orbit.
(b) always experience a net force.
(c) experience equal force in all orbits.
(d) experience maximum force in the outermost orbit.
–
56Bohr Model is valid for only one e system. The energy value allowed for each 5
orbit depends on the principal quantum no. denoted by n. For a multi electron
atom of ion this is not true. The third postulate of Bohr incorporated into
atomic theory which was developed on the basis of Planck and Einstein. We
can determine energies of different energy states, but this requires radius r of
electron orbit.
(i) What is the dependence of angular momentum on radius of the orbit?
(a) Directly proportional
(b) Inversely proportional
(c) Not dependent.
(d) Square of radius.
(ii) What is the second postulate of Bohr?
 (a) The angular momentum is dependent on mass.

(b) Angular momentum is integral multiple of h .

(c) There is no dependence of angular momentum on mass.

(d) All of the above.
(iii) What does the –ve sign in total energy indicates?
(a) Nucleus and e– are repelling each other.
(b) That e– is bound to nucleus.
(c) Both (a) and (b)
(d) None of the above.
(iv) Which of the assumption is deriving for energy of the e– in the orbit?
(a) The energy is dissipated.
(b) Energy is given to make system stable.
(c) e– is stationary.
(d) e– orbit is circular.
Or
(iv) How the frequency of the emitted photon is related to energy difference?
(a) hn = Ei – Ef
(b) hn = Ef – Ei
(c) Ef = Ei – hn
(d) Ef = Ei
57The energy levels of a hypothetical one atoms are shown in figure below: 5
n = ∞ ___________________________ 0 eV
n = 5 ___________________________ –0.80 eV
n = 4 ___________________________ –1.45 eV
n = 3 ___________________________ –3.08 eV
n = 2 ___________________________ –5.30 eV
n = 1 ___________________________ –15.6 eV
(i) What is the ionization potential of the atom?
(a) –15.6 V
(b) 15.6 V
(c) 3.08 V
(d) –3.08 V
(ii) What is the short wavelength limit of the series terminating at n = 2?
(a) l = 1339 Å
(b) l = 4335 Å
(c) l = 2339 Å
(d) l = 1578 Å
(iii) What is excitation potential for the state n = 3?
(a) 3.08 V
(b) 15.6 V
(c) 12.08 V
(d) 12.52 V
 (iv) What is the wave number of the photons emitted for the transition n = 3 to
n=1
(a) 0.009 × 107 m–1
(b) 1.000 × 107 m–1
(c) 1.009 × 10–7 m–1
(d) 1.009 × 107 m–1
Or
(iv) The initial kinetic energy of an electron is 11 eV and it interacts with the
hypothetical one electron atom. What is the minimum energy carried by the
electron after interaction?
(a) 0.7 eV
(b) 1.7 eV
(c) 2.0 eV
(d) 2.1 eV
58The alpha particle scattering experiment by Rutherford made him conclude 5
that most of the space within the atom is empty. The entire positive charge
and most of the mass of the atom is concentrated in its central core. The
angle of scattering of a-particle is dependent on how close to the nucleus, did
it approach. An alpha particle approaching a nucleus slows down and stops at
a certain distance and rebounds back. The angle of scattering keeps on
decreasing due to weaker nuclear repulsive force on them.
(i) The number of a-particles per unit area that scatter at angle θ, varies as,

(ii) The least distance at which an alpha particle stops before reaching a
nucleus is called
(a) distance of scattering
(b) distance of rebounding
(c) distance of closest approach
(d) nuclear radius
(iii) The alpha particles are emitted in this experiment by
(a) charged helium
(b) electric cells
(c) gold foil of 0.1 mm thickness
(d) radioactive source in lead
 (iv) The perpendicular distance of velocity vector of approaching a-particle
from centre of target nucleus is
(a) scattering distance
(b) impact pacometer
(c) trajectory
(d) distance of closest approach
Or
(iv) The electrons revolve around the nucleus in
(a) orbits
(b) form of electron clouds
(c) Both (a) and (b)
(d) None of these.
59According to Bohr’s 3rd postulate of transitions, an electron may make a 5
transition from one of the specified non-radiating orbit to another of lower
energy. When it does so, a photon is emitted having the energy equal to
energy difference between the initial and final state. The frequency of emitted
photon is given by

(i) Which transition belongs to Paschen series?

(a) A
(b) B
(c) C
(d) D
(ii) Which of the transition is found in UV region?
(a) A
(b) B
(c) C
(d) D
(iii) Which transition corresponds to the emission of a spectral line of
wavelength 102.7 nm?
(a) A
(b) B
(c) C
(d) D
(iv) In the given diagram what is the longest wavelength of Balmer series?
(a) 6526.3 Å
(b) 5427.3 Å
(c) 2985.7 Å
 (d) 7468.3 Å
Or
(iv) Who discovered the first spectral series?
(a) Lyman
(b) Balmer
(c) Paschen
(d) P fund
60A photon emitted during the de-excitation of electron from a state n to the first 5
excited state in a hydrogen atom, irradiates a metallic cathode of work
function 2 eV, in a photocell, with a stopping potential of 0.55 V.
(i) To which spectral line series, this transition belong?
(a) Lyman
(b) Balmer
(c) Paschen
(d) Brackett
(ii) In which region does this series lie?
(a) UV region
(b) Visible region
(c) Infrared region
(d) none of these
(iii) What is the ratio of longest to shortest wavelength of this series?
(a) 1 : 3
(b) 5 : 9
(c) 9 : 5
(d) 3 : 1
(iv) What is the value of the quantum number of the state ‘n’?
(a) 1
(b) 2
(c) 3
(d) 4
Or
(iv) The ratio of maximum wavelength to minimum wavelength in Lyman
series is
(a) 4/3
(b) 3/4
(c) 1/3
(d) 1/4
61 In terms of Rydberg constant R, the wave number of the first Balmer line is 1
62The ionisation energy of hydrogen atom is 13.6 eV. Following Bohr’s theory the 1
energy corresponding to a transition between 3rd and 4th orbits is
(a) 3.40 eV (b) 1.51 eV
(c) 0.85 eV (d) 0.66 eV
63 The energy of hydrogen atom in the nth orbit is En, then the energy in the nth 1
orbit of single ionised helium atom is

64 The spectral lines in the Brackett series arise due to transition of electron in 1
hydrogen atom from higher orbits to the orbit with
(a) n = 1 (b) n = 2
(c) n = 3 (d) n = 4
65 On moving up in the energy states of a H-like atom, the energy difference 1
between two consecutive energy states
(a) decreases.
(b) increases.
(c) first decreases then increases.
(d) first increases then decreases.
66 The transition of electron from n = 4, 5, 6, ...... to n = 3 corresponds to 1
(a) Lyman series (b) Balmer series
(c) Paschen series (d) Brackett series
67As per Bohr model, the minimum energy (in eV) required to remove an 1
electron from the ground state of double ionized Li atom (Z = 3) is
(a) 1.51 eV
(b) 13.6 eV
(c) 40.8 eV
(d) 122.4 eV
68 Which of the following spectral series in hydrogen atom gives spectral line of 1
4860 Å?
(a) Lyman
(b) Balmer
(c) Paschen
(d) Brackett

69 In terms of Rydberg constant R, the shortest wavelength in Balmer series of 1

hydrogen atom spectrum will have wavelength
 ++
70 Taking the Bohr radius as a0 = 53 pm, the radius of Li ion in its ground state, 1
on the basis of Bohr’s model, will be about
(a) 53 pm (b) 27 pm
(c) 18 pm (d) 13 pm
71The simple Bohr model cannot be directly applied to calculate the energy 1
levels of an atom with many electrons. This is because [NCERT Exemplar]
(a) of the electrons not being subject to a central force.
(b) of the electrons colliding with each other.
(c) of screening effects.
(d) the force between the nucleus and an electron will no longer be given by
Coulomb’s law.
72For the ground state, the electron in the H-atom has an angular momentum = 1
according to the simple Bohr model. Angular momentum is a vector and
hence there will be infinitely many orbits with the vector pointing in all
possible directions. In actuality, this is not true,
(a) because Bohr model gives incorrect values of angular momentum.
(b) because only one of these would have a minimum energy.
(c) angular momentum must be in the direction of spin of electron.
(d) because electrons go around only in horizontal orbits.
73 O2 molecule consists of two oxygen atoms. In the molecule, nuclear force 1
between the nuclei of the two atoms
(a) is not important because nuclear forces are short-ranged.
(b) is as important as electrostatic force for binding the two atoms.
(c) cancels the repulsive electrostatic force between the nuclei.
(d) is not important because oxygen nucleus has equal number of neutrons
and protons.
74Two H atoms in the ground state collide inelastically. The maximum amount 1
by which their combined kinetic energy is reduced is
(a) 10.20 eV (b) 20.40 eV
(c) 13.6 eV (d) 27.2 eV
75 A set of atoms in an excited state decays. [NCERT Exemplar] 1
(a) in general to any of the states with lower energy.
(b) into a lower state only when excited by an external electric field.
(c) all together simultaneously into a lower state.
(d) to emit photons only when they collide.
76An ionised H-molecule consists of an electron and two protons. The protons 1
are separated by a small distance of the order of angstrom. In the ground
state, [NCERT Exemplar]
(a) the electron would move in circular orbits.
(b) the energy would be (2)4 times that of a H-atom.
(c) the electrons, orbit would go around the protons.
(d) the molecule will soon decay in a proton and a H-atom.
77 The Balmer series for the H-atom can be observed 1
(a) if we measure the frequencies of light emitted when an excited atom falls
to the ground state.
(b) if we measure the frequencies of light emitted due to transitions between
excited states and the first excited state.
(c) in any transition in a H-atom.
(d) as a sequence of frequencies with the lower frequencies getting closely
packed.
78 1
Let En = be the energy of the nth level of H-atom. If all the H-atoms

are in the ground state and radiation of frequency (E2 – E1)/h falls on it,
(a) it will not be absorbed at all.
(b) some of atoms will move to the first excited state.
(c) all atoms will be excited to the n = 2 state.
(d) all atoms will make a transition to the n = 3 state.
79 The Bohr model of an atom 1
(a) assumes that the angular momentum of electrons is quantised.
(b) uses Einstein’s potoelectric equation.
(c) predicts continuous emission spectra for atoms.
(d) predicts the same emission spectra for all types of atoms.
80 For ionising an exicited hydrogan atom, the energy required (in eV) will be 1
(a) a little less than 13.6 eV
(b) 13.6 eV
(c) more than 13.6 eV
(d) 3.4 or less
81 The electrons in the Bohr’s orbit have 1
(a) K.E. greater than P.E.
(b) P.E. greater than K.E.
(c) the same values
(d) none of these
82The binding energy of a H-atom, considering an electron moving around a 1
fixed nuclei (proton), is

B=– (m = electron mass)

If one decides to work in a frame of reference where the electron is at rest, the
proton would be moving arround it. By similar arguments, the binding energy
would be
B=– (M = proton mass)
This last expression is not correct because
(a) n would not be integral.
(b) Bohr-quantisation applies only to electron.
(c) the frame in which the electron is at rest is not inertial.
 (d) the motion of the proton would not be in circular orbits, even
approximately.
83Consider aiming a beam of free electrons towards free protons. When they 1
scatter, an electron and a proton cannot combine to produce a H-atom,
(a) because of energy loss.
(b) without simultaneously releasing energy in the from of radiation.
(c) because of momentum conservation.
(d) because of angular momentum conservation.
84 The Bohr model for the spectra of a H-atom 1
(a) will be applicable to hydrogen in the molecular from.
(b) will not be applicable as it is for a He-atom.
(c) is valid only at room temperature.
(d) predicts continuous as well as discrete spectral lines.
4
85 The simple Bohr model is not applicable to He atom because 1
(a) He4 is an inert gas.
(b) He4 has neutrons in the nucleus.
(c) He4 has one electron.
(d) electrons are not subject to central forces.
86 Fill in the blanks. 1
(i) Pfund series of line spectrum of hydrogen atom belongs to __________
region.
(ii) The ground state energy of hydrogen atom is __________ eV.
(iii) Photon of maximum frequency is obtained from transition of electron
from __________ to of hydrogen like atom.
87A hydrogen atom makes a transition from n = 5 to n = 1 orbit. The wavelength 1
of photon emitted is λ. The wavelength of photon emitted when it makes a
transition from n = 5 to n = 2 orbit is

88Read the following statements carefully. 1

(i) Only charged particles at rest are accompanied by matter waves.
(ii) Any particle in motion, whether charged or uncharged, is accompanied by
matter waves.
(iii) The associated wavelength with proton is shorter than that of electron,
both moving with same speed.
(iv) de Broglie wavelength associated with the matter wave of a charged
particle is directly proportional to the potential difference through which it is
accelerated.
Identify the correct statements.
(a) (ii) and (iii) only
(b) (i) and (ii) only
 (c) (i), (ii) and (iv) only
(d) only (ii) is correct
89 Write two important limitations of Rutherford nuclear model of the atom. 2

90For the following questions, two statements are given-one labelled Assertion 1
(A) and the other labelled Reason (R). Select the correct answer to these
questions from the codes (a), (b), (c) and (d) as given below.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is NOT the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.
Assertion: The total energy of revolving electron in any stationary orbit is
negative.
Reason: Energy is a scalar quantity. It can have positive or negative values.

91For the following questions, two statements are given-one labelled Assertion 1
(A) and the other labelled Reason (R). Select the correct answer to these
questions from the codes (a), (b), (c) and (d) as given below.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is NOT the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.
Assertion: Nuclear density is extremely large.
Reason: Most mass of the atom is concentrated in the nucleus, but its volume
is 10–15 times smaller compared to volume of the atom..
92For the following questions, two statements are given-one labelled Assertion 1
(A) and the other labelled Reason (R). Select the correct answer to these
questions from the codes (a), (b), (c) and (d) as given below.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is NOT the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.
Assertion: An electron in hydrogen atom passes from n = 3 to n = 1 level. The
maximum number of photons emitted is 3.
Reason: The number of photons emitted can be calculated using the

expression

93For the following questions, two statements are given-one labelled Assertion 1
(A) and the other labelled Reason (R). Select the correct answer to these
questions from the codes (a), (b), (c) and (d) as given below.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is NOT the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.
 Assertion: Total energy of revolving electron in any >stationary orbit is
negative.
Reason: Energy is a scalar quantity. It can have only positive values.

94For the following questions, two statements are given-one labelled Assertion 1
(A) and the other labelled Reason (R). Select the correct answer to these
questions from the codes (a), (b), (c) and (d) as given below.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is NOT the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.
Assertion: The classical Rutherford model for atom of electron orbiting
around the nucleus, does not explain the atomic structure.
Reason: The atom emits energy due to orbiting electron and remains in a
stable state.
95For the following questions, two statements are given-one labelled Assertion 1
(A) and the other labelled Reason (R). Select the correct answer to these
questions from the codes (a), (b), (c) and (d) as given below.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is NOT the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.
Assertion: In Lyman series, the ratio of minimum and maximum wavelength is
3/4.
Reason: Lyman series constitute spectral lines corresponding to transition
from high energy to ground state of hydrogen atom.
96 If 13.6 eV energy is required to ionise the hydrogen atom, then energy 1
required to remove an electron from n = 2 is
(a) 10.2 eV (b) 0 eV
(c) 3.4 eV (d) 6.8 eV
97 In Bohr’s model of an atom which of the following is an integral multiple of 1

?
(a) Kinetic energy (b) Radius of an atom
(c) Potential energy (d) Angular momentum
98The transition from the state n = 5 to n = 1 in a hydrogen atom results in UV 1
radiation. Infrared radiation will be obtained in the transition
(a) 2 → 1 (b) 3 → 2
(c) 4 → 3 (d) 6 → 2
99 In Bohr’s model, the atomic radius of the first orbit is r0. Then, the radius of 1
the third orbit is
(a) r0/9
(b) r0
(c) 9r0
 (d) 3r0
100 The K.E. of the electron in an orbit of radius r in hydrogen atom is 1
proportional to

101The hydrogen atom can give spectral lines in the Lyman, Balmer and 1
Paschen series. Which of the following statement is correct?
(a) Lyman series is in the infrared region.
(b) Balmer series is in the visible region.
(c) Paschen series is in the visible region.
(d) Balmer series is in the ultraviolet region.
102 The ratio between Bohr radii is 1
(a) 1 : 2 : 3 (b) 2 : 4 : 6
(c) 1 : 4 : 9 (d) 1 : 3 : 5
103Which of the relation is correct between time period and number of orbits 1
while an electron is resolving in an orbit?

104Energy of an electron in the second orbit of hydrogen atom is E and the 1

energy of electron in 3rd orbit of He will be

105 The longest wavelength in Balmer series of hydrogen spectrum will be 1

(a) 6557 Å (b) 1216 Å
(c) 4800 Å (d) 5600 Å