CHEM 151 TRIAL QUESTIONS

1. When an electron drops from a higher energy level to a low energy level then

(a) energy is emitted

(b) energy is absorbed

(c) atomic number increase

(d) atomic number decrease

2. Of the following the one that is not an elementary particle is

(a) proton

(b) neutron

(c) -particle

(d) electron

3. A helium molecule of 30k is moving with a velocity of 2.4 x 10 2ms-1. The de-Broglie wave length
is about

(a) 0.416 nm

(b) 0.83 nm

(c) 803 A0

(d) 800 Ao

4. The energy equivalent of the rest mass of an electron (9.1×10 -31 kg)

(a) 8.1 J
(b) 27.3 x 10-10J

(c) 8.1x 10-11 J

(d) 8.1x 10-14 J

5. Using arbitrary energy units, it is calculated that 80 arbitrary units (a.u) are needed to transfer
electron in a hydrogen atom from the most stable Bohr orbit to a large distance from the nucleus

(a) 5a.u

(b) 10a.u.

(c) 20a.u.

(d) 40a.u.

6. Isotonic are atoms having the same

(a) atomic mass

(b) mass number

(c) atomic number

(d) number of neutrons

7. The particle discovered in the anode ray experiments is the

(a) Neutron

(b) Proton

(c) Electron

(d) Meson
 8. The number of protons present in the atom of an element is known as the

(a) Atomic Weight

(b) Proton Number

(c) Proton Number

(d) Atomic Number

9. The smallest particle of an element which can take part in chemical reactions and may or may
not exist independently is the

(a) Nucleus

(b) Atom

(c) Neutron

(d) compound

10. The sum of the numbers of the protons and neutrons in the atom of an element is known as

(a) Mass Number

(b) Isotope Number

(c) Molecular Weight

(d) Atomic Number

11. The charge on the electron was discovered by

(a) J. J. Thomson

(b) Mullikan
(c) Fermi

(d) Faraday

12. The Atomic Theory was given by

(a) J. J. Thomson

(b) E. Rutherford

(c) James Chadwick

(d) John Dalton

13. According to Rutherford,

(a) the protons revolves around the nucleus

(b) the nucleus revolves around the electrons

(c) the neutrons revolve around the nucleus.

(d) the electrons revolve around the nucleus.

14. The alpha particle scattering experiment was carried out by

(a) J. J. Thomson

(b) E. Goldstein

(c) J. Chadwick

(d) E. Rutherford
15. As a result of Rutherford's scattering experiment, it was concluded that

(a) the center of the atom is empty

(b) most of the atom is empty
(c) the center of the atom has a negative charge.
(d) atomic mass is spread over the whole atom.

16. The particle discovered as a result of cathode ray experiments is the

(a) nucleus
(b) proton
(c) neutron
(d) electron

17. The three fundamental particles of the atom are

(a) Positron, Neutrino and Gamma Rays
(b) Mesons, Quarks and Anti-neutrino
(c) Nucleus, Anti-quarks and Electrons
(d) Proton, Neutron and Electron

18. The charge by mass ratio for electrons of various elements

(a) increases with increase in atomic mass.
(b) decreases with increase in atomic mass.
(c) increases with increase in atomic number.
(d) is the same

19. The charge on the electron was discovered by

(a) Faraday
(b) Fermi
(c) Mullikan
(d) J. J Thomson

20. According to Rutherford, the atom consists of the following two parts
(a) Electrons and Protons
(b) Protons and Neutrons
(c) Neutrons and Electrons
(d) Nucleus and the extra-nuclear part
21. The currently accepted model of the atom is that of
(a) Bohr
(b) de Broglie
(c) Rutherford
(d) Heisenberg

22. Neutron was discovered by

(a) E. Goldstein
(b) John Dalton
(c) E. Rutherford
(d) James Chadwick

23. Huygens Wave Theory could not explain, ____

(a) All these
(b) Polarization
(c) Compton Effect
(d) Photoelectric Effect

24. The Drawbacks of Newton’s Corpuscular Theory is that it cannot explain

______
(a) Interference
(b) Diffraction
(c) Polarization
(d) All of above
(e) None of above

25. According to Max Planck’s Quantum Theory, radiation is not continuous,

but discontinuous packets of light called _______
(a) Photons
(b) energy
(c) electromagnetic radiation

26. A wave is called periodic if:

a). disturbance is repeated in equal time intervals
b. disturbance is repeated in very long time intervals
c. disturbance is repeated in short time intervals African Virtual University

27. The wavelength is defined as:

a. the distance traveled by a progressive wave in a second
b. the distance traveled by a progressive wave in a period
c. the distance traveled by a progressive wave in a half period

28. The frequency of a wave is expressed as:

a. second
b. Hertz
c. meter

29. The electromagnetic wave is due to the spread of:

a. an electrical disturbance in a material medium
b. a magnetic disturbance in a material medium
c. an electromagnetic field

30. The speed of propagation of an electromagnetic wave in vacuum is:

a. 3 x 10 6 m/s
b. 3 x 10 8 m/s
c. 3 x 10 8 km/s

31. If the frequency of an electromagnetic wave in vacuum is 600 kHz, its

wavelength is equal to:
a. 500 m
b. 2000 m
c. 5 km

32. Calculate the energy (J) change associated with an electron transition
from n = 2 to n = 5 in a Bohr hydrogen atom.
A) 6.5 × 10-19
B) 5.5 × 10-19
C) 8.7 × 10-20
D) 4.6 × 10-19
E) 5.8 × 10-53

33. The frequency of electromagnetic radiation required to promote an

electron from n = 2 to n = 4 in a Bohr hydrogen atom is __________ Hz.
A) 4.13 × 10-19
B) 6.17 × 1014
C) 5.46 × 10-19
D) 8.22 × 1014
E) 4.13 × 1019

34. A spectrum containing only specific wavelengths is called a __________

spectrum.
A) line
B) continuous
C) visible
D) Rydberg
E) invariant
35. The n = 2 to n = 6 transition in the Bohr hydrogen atom corresponds to
the __________ of a photon with a wavelength of __________ nm.
A) emission, 410
B) absorption, 410
C) absorption, 660
D) emission, 94
E) emission, 390

36. The n = 5 to n = 3 transition in the Bohr hydrogen atom corresponds to

the __________ of a photon with a wavelength of __________ nm.
A) absorption, 657
B) absorption, 1280
C) emission, 657
D) emission, 1280
E) emission, 389

37. The potential energy of interaction between two static charges is:
a. proportional to the distance separating the two charges
b. inversely proportional to the distance separating the two charges
c. inversely proportional to the square of the distance separating the two

38. The expression of the momentum of a photon is :

a. p = h λ

b. p = h / λ

c. p = c/λ

39. The energy of a photon, expressed in eV, the visible light of wavelength
λ = 634 nm is equal to:

a. E = 1.95 eV

b. E = 19.5 eV

c. E = 0.195 eV

40. The wavelength, expressed in nm, of a photon of energy equal to 1 keV

is equal to:

a. λ = 0.124 nm ;
b. λ = 1.24 nm ;

c. λ = 12.407 nm

42. The n = 8 to n = 4 transition in the Bohr hydrogen atom occurs in the

__________ region of the electromagnetic spectrum.
A) infrared
B) visible
C) ultraviolet
D) microwave
E) X-ray

43. The n = 8 to n = 2 transition in the Bohr hydrogen atom occurs in the

__________ region of the electromagnetic spectrum.
A) radio
B) X-ray
C) infrared
D) microwave
E) ultraviolet

44. At what speed (m/s) must a 3.0-mg object be moving in order to have a
de Broglie wavelength
of 5.4 × 10-29 m?
A) 1.6 × 10-28
B) 3.9 × 10-4
C) 2.0 × 1012
D) 4.1
E) 6.3

45. The wavelength associated with an electron of energy E = 100 eV is equal to :

a. 1.23nm

b. 12.3 nm

c. 123 nm

46. The wavelength associated with a 2 g ball with a velocity of 100 m/s is equal to:
a. 3.31x10-33 m

b. 3.31x10-30 m

c. 2.38x10-24 m

47. According to the theory of Bohr, the energy values of the electron in a hydrogen atom is given
by:

a. En=- 13.58 /n eV ;

b. En=- 13.58 /n2 eV ;

c En=13.58 /n2 eV

n being a positive integer : n = 1,2,3,…..∞

48. The energy of photon emitted by one atom Bohr making a transition state with quantum
number n = 5 to the state of quantum number n = 4 is equal to:

a. 0.55 eV

b. 0.68 eV

c. 0.30 eV

49. A Bohr atom initially in its ground state makes a transition to its first excited state after
absorbing a photon. What is the wavelength of the photon absorbed?

a. 55 nm

b. 122 nm

c. 181nm

50. The largest wavelength of the Balmer series is equal to:

a. 365 nm

b. 434 nm

c. 175nm

51. The energy of an electron in the first orbit of hydrogen is 13.6eV. Which one of the following is
the second excited state of electron in hydrogen atom?

a. -3.4eV
b. -6.8eV

c. -1.5Ev

d. +3.4eV

52. The wave number of the first line in the Balmer series of hydrogen is 15200cm-1. The
wavenumber of the first line in the Balmer series of Be3+ would be

a. 60800cm-1

b. 2.432 x 105

c. 3800cm-1

d. 950cm-1

53. The wavenumber of the radiation emitted when the electron jumps from fourth energy level
to second energy level in He+ is about

a. 20565 cm-1
b. 41030 cm-1
c. 82258 cm-1
d. 5141 cm-1

54. The wave number of an electromagnetic radiation is 1x105 cm-1. The frequency of the
radiation would be

a. 3x108s-1

b. 3x106s-1

c. 3x1010s-1

d. 3x1015s-1

55. When an electronic transition occurs in an atom from higher energy state to lower energy
state with energy difference equal to ∆E electron volts, the wavelength of the radiation emitted is
approximately equal to

a. 12397x10-10m
∆E

B. 12397x10-10A
∆E
C. 12397x10-10cm
∆E

D. 12397x1010cm
∆E

56. What are the speed and momentum of a 500-nm photon?

(a) 2.998 x 108 m/s, 133 x 10-30 kg·m/s

(b) 2.998 x 108 m/s, 133 x 10-27 kg·m/s
(c) 2.998 x 108 m/s, 7.52 x 106 kg·m/s
(d) 2.998 x 108 m/s, 133 x 10-36 kg·m/s

57. Compute the de Broglie wavelength of an electron that has been accelerated through a
potential difference of 9.0 kV. Ignore relativists effects.

(a) 1.3 x 10-11 m

(b) 1.7 x 10-22 m
(a) 1.2 x 10-26 m
(b) 5.2 x 10-21 m

58. The wave-particle duality theory is the first to give an adequate explanation of which of the
following facts about the hydrogen atom?

(a) Why more than one possible orbit exists for the electron.
(b) Why only certain energies are possible for the orbiting electron.
(c) Why more than one momentum is possible for the orbiting electron.
(d) None of these are correct

59. The concept of dual nature of radiation was introduced by,

(a) Einstein
(b) Max Planck
(c) De Broglie
(d) H.G.J. Mosley

60. Rutherford’s experiment of a-particles showed for the firs time that atom has

(a) Protons
(b) Neutrons
(c) Nucleus
 (d) Electrons

61. Which of the following transitions will emit maximum energy in the hydrogen atom?

(a) 4f 2s
(b) 4d 2p
(c) 4p 2s
(d) All have same energy

62. The wavelength of a spectral line for electron transition in an atom is inversely proportional to

(a) velocity of electron

(b) number of electrons undergoing transition
(c) the difference of energy between energy levels involved in the transition
(d) the difference of energy between energy levels involved in the transition

63. The de Broglie equation suggests that an electron has

(a) particle character

(b) wave character
(c) particle as well as wave character
(d) none of the above statements is true

64. The value of Bohr’s radius of hydrogen atom is

(a) 0.529 x 10-6cm

(b) 0.529 x 10-6m
(c) 0.529 x 10-10cm
(d) 0.529 x 10-10m

65. Copper consists of 69.1% Cu-63 and 30.9% Cu-65. Calculate the relative atomic mass, Ar, of
copper to 3sf/1dp.

A. 6

B. 64.0

C. 63.6

D. 63.3

66. Bromine consists of the isotopes: 50.5% Br-79 and 49.5% Br-81. Calculate the relative atomic
mass, Ar, of bromine to 3sf/1dp.
 A. 80.0

B. 80.1

C. 79.9

D. 79.8

67. Iron has four stable isotopes. 5.8% Fe-54, 91.7% Fe-56, 2.2% Fe-57 and 0.3% Fe-58. Calculate
the Ar of iron to 3sf/1dp.

A. 55.9

B. 56.1

C. 56.2

D. 56.3

68. Antimony (Sb) is 57.2% Sb-121 and 42.8% Sb-123. Calculate the Ar of Sb to 4sf/1dp.

A. 121.2

B. 121.9

C. 122.1

D. 122.0

69. Boron is 19.7% B-10 and 80.3% B-11. Calculate the relative atomic mass, Ar, of boron to
3sf/1dp.

A. 10.3

B. 10.9

C. 10.5

D. 10.8

70. The atomic mass of titanium is 47.88 atomic mass units. This atomic mass represents
(a) weighted average mass of the most abundant isotope of Ti
(b) total mass of all the protons, neutrons, and electrons in an atom of Ti
(c) total mass of all the protons and neutrons in an atom of Ti
(d) weighted average mass of all the naturally occurring isotopes of Ti
71. The average isotopic mass of chlorine is 35.5. Which mixture of isotopes (shown as percents)
produces this average mass?

(a) 75% Cl-35 and 25% Cl-37

(b) 50% C-12 and 50% C-13

(c) 50% Cl-35 and 50% Cl-37

(d) 75% C-12 and 25% C-13

72. Calculate the wavelength of the lowest energy transition in the Brackett series of the
electronic spectrum of the Li+ ion. The Rydberg constant for He is RLi = 109729 cm-1.
(a) 450 nm
(b) 4050nm
(c) 91.1 nm
(d) 30.3 nm

73. A line in the Paschen series of the emission spectrum of atomic hydrogen is observed at a
wavenumber of 7800 cm-1. Deduce the upper state principal quantum number for this transition.
(a)7
(b) 6
(c) 4
(d) 2

74. Calculate, from the fundamental constants, the value of the Rydberg constant for a deuterium
atom.

(a) 109677 cm-1

(b) 109707 cm-1
(c) 109722 cm-1
(d) 109729 cm-1

75.What is the longest wavelength in the Lyman Series?

(A) 45.60 nm.

(B) 91.20 nm.

(C) 121.5 nm.

(D) 240.1 nm.

(E) 356.2 nm.

76. To which of the following values of n does the longest wavelength in the Balmer series
correspond? (A) 1.

(B) 3.

(C) 5.

(D) 7.

(E) ∞

77. What energy photon emitted is when an electron in a hydrogen atom goes from the n= 5
energy level to the n= 2 energy level?

(a) 10.20 eV

(b) 13.60 eV

(c) 6.80 eV

(d) 2.86 eV

78. Calculate the de Broglie wavelength of a 0.145 kg baseball moving at a speed of 45.2 m/s
(≈101 mph).

(a) 1.01 × 10−34 m

(b) 2.62 × 10−24 m

(c) 3.17 × 10−9 m

(d) 4.58 × 10−2 m

79. In the spectrum of hydrogen atom, the series which falls in ultraviolet region is

(a) Lyman series

(b) Balmer series

(c) Paschen series

(d) Brackett series

80. The Balmer series in the spectrum of hydrogen atom falls in

(a) ultraviolet region

(b) visible region

(c) infrared region

(d) none of these

81. Lyman series is obtained when the electrons from higher energy levels return to

(a) 1st orbit

(b) 2nd orbit

(c) 3rd orbit

(d) 4th orbit

82. A line in Pfund series is obtained when an electron from higher energy levels returns to

(a) 1st orbit

(b) 3rd orbit

(c) 5th orbit

(d) 6th orbit

83. The energy of an electron in Bohr’s atom _______ as we move away from the nucleus

(a) remains the same

(b) decreases

(c) increases

(d) sometimes increases, sometimes decreases

84. When an electron drops from a higher energy level to a lower energy level, then

(a) the energy is absorbed

(b) the energy is released

c) the nuclear charge increases

(d) the nuclear charge decreases

85. The energy of an electron in the first Bohr orbit for hydrogen is

(a) 13.6 eV

(b) –13.6 eV

(c) 1.36 eV

(d) –1.36 eV

86. The spectral line lies in the Lyman series. It corresponds to the radiation emitted by an
electron jumping from higher energy sates to

(a) first energy state

(b) second energy state

(c) third energy state

(d) fifth energy state

87. The ground state of an atom corresponds to a state of

(a) maximum energy

(b) minimum energy

(c) zero energy

(d) negative energy

88. Balmer series in the spectrum of hydrogen atom lies in

(a) ultraviolet region

(b) visible region

(c) infrared region

(d) none of these

89. The spectrum of hydrogen atom is similar to that of

(a) H+ ion

(b) He+ ion

c) Li+ ion

(d) Na+ ion

90. If r is the radius of first orbit, the radius of nth orbit of hydrogen atom will be

(a) n2 r

(b) n r

c) n/r

(d) r/n

91. The ratio of radii of second and first orbit of hydrogen atom according to Bohr’s model is

(a) 2:1

(b) 1:2

(c) 4:1

(d) 1:4

92. In Bohr’s model of atom, the angular momentum of an electron orbiting around the nucleus is
given by the relation

(a ) mvr = h
2π

(b) mvr = nh
2π

(c) mvr = n2h2

4π
(d) mvr = nh
4π

93. The radius of first orbit in hydrogen atom according to Bohr’s Model is given by the relation

(a) r = h2
4π2m e2

(b) r = h2
4π2m e2

(c) r = h2
4π2m e2

(d) r = h2
4π2m e2

94. The radius of first orbit in hydrogen atom is 0.529 Å. The radius of second orbit is given by

(a) ½ × 0.529 Å

(b) 2 × 0.529 Å

c) 4 × 0.529 Å

(d) 8 × 0.529 Å

95. The energy of an electron in the first orbit in hydrogen atom is –313.6/n2 kcal mol–1. The
energy of the electron in 3rd orbit is given by the relation

(a) E3 = 313.6 1 kcal mol-1

3

(b) E3 = 313.6 1 kcal mol-1

2
(c) E3 = 313.6 1 kcal mol-1
9

(d) E3 = 313.6 3 kcal mol-1

96. Of the following, __________ radiation has the shortest wavelength.

A) X-ray
B) radio
C) microwave
D) ultraviolet
E) infrared

97. Which one of the following is considered to be ionizing radiation?

A) visible light
B) radio waves
C) X-rays
D) microwaves
E) infrared radiation

98. Of the following transitions in the Bohr hydrogen atom, the __________ transition results in
the emission of the highest-energy photon.
A) n = 1 → n = 6
B) n = 6 → n = 1
C) n = 6 → n = 3
D) n = 3 → n = 6
E) n = 1 → n = 4

99. Of the following transitions in the Bohr hydrogen atom, the __________ transition results in
the emission of the lowest-energy photon.
A) n = 1 → n = 6
B) n = 6 → n = 1
C) n = 6 → n = 3
D) n = 3 → n = 6
E) n = 1 → n = 4

100. In the Bohr model of the atom, __________.

A) electrons travel in circular paths called orbitals
B) electrons can have any energy
C) electron energies are quantized
D) electron paths are controlled by probability