TAURIAN WORLD SCHOOL

Annual Examination (2024-25 )

CLASS – XI MM:70

SUB - CHEMISTRY TIME: 3 Hr

General Instructions:

Read the following instructions carefully and follow them:

This question paper contains 33 questions. All questions are compulsory.

1. This question paper is divided into five sections – Sections A, B, C, D and
E.
2. In Section A – Questions no. 1 to 16 are Multiple Choice type questions.
Each question carries 1 mark.
3. In Section B – Questions no. 17 to 21 are Very Short Answer type
questions.
Each question carries 2 marks
4. In Section C – Questions no. 22 to 28 are Short Answer type questions.
Each
Question carries 3 marks
5. In Section D – Questions no. 29 and 30 are case study-based questions.
Each question carries 4 marks.
6. In Section E – Questions no. 31 to 33 are Long Answer type questions.
Each
Question carries 5 marks
7. There is no overall choice given in the question paper. However, an
internal
Choice has been provided in few questions in all the Sections except
Section A
8 The use of log table and calculation is not allowed
9 All question are compulsory
 Section A

1. A pure substance which contains only one type of atom is called

————–.
(a) An element
(b) a compound
(c) a solid
(d) a liquid
2. The smallest particle that can take part in chemical reactions is ————–.
(a) Atom
(b) molecule
(c) Both (a) and (b)
(d) none of these

3. Which of the following is a homogeneous mixture?

(a) Mixture of soil and water
(b) Sugar solution
(c) Mixture of sugar, salt and sand
(d) Iodized table salt
4.The significant figures in 0.00051 are ————–.
(a) 5
(b) 3
(c) 2
(d) 26
5. Neutron was discovered by ————–
(a) J.J Thomson
(b) Chadwick
(c) Rutherford
(d) Priestley
6. The nucleus of the atom consists of ————–
(a) Protons and neutrons
(b) Protons and electrons
(c) Neutrons and electrons
(d) Protons, neutrons and electrons
7. The radius of an atomic nucleus is of the order of————–
(a) 10-10 cm
(b) 10-13 cm
(c)10-15 cm
(d) 10-8 cm
8. Isotopes of an element have ————–
(a) Different chemical and physical properties
(b) Similar chemical and physical properties
(c) Similar chemical but different physical properties
(d) Similar physical but different chemical properties

9. The vertical columns in the periodic table are termed as ———-.

(a) periods
(b) groups
(c) series
(d) none of these
10. The element with atomic number 26 will be found in group :
(a) 2
(b) 8
(c) 6
(d) 10
11. The elements with atomic numbers 9, 17, 35, 53, 85 are all ———-
(a) halogens
(b) noble gases
(c) alkali earth metals
(d) transition metals
12. Which of the following is not a redox reaction?
(a) Burning of candle
(b) Rusting of iron
(c) Dissolving salt in water
(d) Dissolving Zinc in dil. H2SO4

13. The oxidation number of Cr in Cr(CO)6 is —————–

(a) 0
(b) +2
(c) -2
(d) +6
14. Which of the following is not a redox reaction?
(a) CaCO3 → CaO + CO2
(b) O2 + 2H2 → 2H2O
(c) Na + H2O → NaOH + 1/2H2
(d) MnCl3 → MnCl2 + 1/2 Cl2
15. In the reaction
3Br2 + 6CO32- + 3H2O → 5Br – + BrO3– + 6HCO3–
(a) Bromine is oxidised and carbonate is reduced.
(b) Bromine is reduced and water is oxidised.
(c) Bromine is neither reduced nor oxidised.
(d) Bromine is both reduced and oxidised.
16. The most powerful oxidising agent among the following is:
(a) H2SO4
(b) H3BO3
(c) HPO3
(d) H3PO4

Section -B

17. What will be the mass of one atom of C-12 in grams?

18. Arrange s, p and d sub-shells of a shell in the increasing order of effective
nuclear charge (Zeff) experienced by the electron present in them.
19. Explain why the electron gain enthalpy of fluorine is less negative than that
of chlorine.
20. Explain why PCl5 is trigonal bipyramidal whereas IF5 is square pyramidal.
21. The reaction
Cl2 (g) + 2OH– (aq) → CIO– (aq) + Cl– (aq) + H2O(l)
Represents the process of bleaching. Identify and name the species that
bleaches the substances due to their oxidizing action.
Section –C
22. 45.4 L of dinitrogen reacted with 22.7 L of dioxygen and 45.4 L of nitrous
oxide was formed. The reaction is given below:
2N2(g) + O2(g) → 2N2O(g)
Which law is being obeyed in this experiment? Write the statement of the law.
23. The Balmer series in the hydrogen spectrum corresponds to the transition
from n₁ = 2 to n₂ = 3, 4,… This series lies in the visible region. Calculate the wave
number of the line associated with the transition in the Balmer series when the
electron moves to n = 4 orbit. (RH = 109677 cm-¹)
24. Write four characteristic properties of p-block elements.
25. In both water and dim ethyl ether (CH3–O–CH3), oxygen atom is central
atom, and has the same hybridization, yet they have different bond angles.
Which one has a greater bond angle? Give reason.

26. PbO and PbO₂ react with HCl according to the following chemical equations:
2PbO + 4HCl → 2PbCl2 + 2H2O
PbO2 + 4HCI → PbCl2 + Cl2 + 2H2O
Why do these compounds differ in their reactivity?
27. Nitric acid is an oxidising agent and reacts with PbO, but it does not react
with PbO₂. Explain why?
28. The effect of the uncertainty principle is quite significant only for the motion
of microscopic particles and is negligible for the given macroscopic particles.
Explain the statement with the help of a suitable example.
Section D
29. Orbitals are region or space wher.e there is maximum probability of finding
electrons. Qualitatively, these orbitals can be distinguished by their size, shape
and orientation. An orbital of small size means there is more chance of finding
the electron near the nucleus. Shape and orientation means the direction in
which probability of finding electron is maximum. Atomic orbitals can be
distinguished by quantum numbers. Each orbital is designated by three
quantum numbers n, I and m1 (magnetic quantum number) which define
energy, shape and orientation but these are not sufficient to explain spectra of
multi-electrons atoms. Spin quantum number (ms ) determines the spin of
electron. Spin angular momentum of electron has two orientations relative to
chosen axis which are distinguished by spin quantum numbers m s which can
take values +1/2 and -1/2.
Value of 'l' 01 234
Notation for subshell s pd f g
(a) How many orbitals are associated with n = 3?
(b) Describe the orbitals represented by (i) n = 2, l = 1 (ii) n = 4, l = 0.
 (c) How many electron are possible in an orbital? Why?
(d) What is shape of 's' and 'p' orbitals?
(e) Name two d-orbitals which are on axis.

30. The attractive force which holds the two atoms together is called chemical
bond. Covalent bond is formed by equal sharing of electrons. Coordinate bond is
formed by unequal sharing of electrons. Ionic bond is formed by transfer of
electrons from one atom to another. Octet rule, although very useful but it is
not universally applicable. According to valence bond theory, covalent bond is
formed by overlapping of half filled atomic orbitals resulting in lowering of
energy and more stability. Bond order is the number of bonds between atoms in
a molecule. Higher the bond order, more will be stability and bond dissociation
enthalpy but smaller bond length. Polarity of covalent bond depends upon
difference in electronegativity. Covalent character of bond depends upon
polarising power, smaller cation and bigger anions have higher polarising
power. VSEPR theory helps to predict shapes of molecules.

(a) Write the, electron dot structure of N2O.

(b) What are ions present in CsI3?
(c) Out of CN+, CN-, NO, which has highest bond order?
(d) What is correct order of repulsion bp - bp, lp - lp and lp - bp?
(e) Draw the structure of XeOF4 on the basis of VSEPR theory.
(f) Which out of B2 ,CO, O2−2O22− and NO+ are paramagnetic and why?
Section E
31. A vessel contains 1.6 g of dioxygen at STP (273.15K, 1 atm pressure). The gas
is now transferred to another vessel at a constant temperature, where pressure
becomes half of the original pressure. Calculate
(i) volume of the new vessel.
(ii) number of molecules of dioxygen.
32. Why was a change in the Bohr Model of atom required? Due to which
important development (s), the concept of movement of an electron in an orbit
was replaced by, the concept of probability of finding an electron in an orbital?
What is the name given to the changed model of the atom?
33. Why does fluorine not show a disproportionation reaction?

Answer key

1) An element
2) (c) Both (a) and (b)
3) Sugar solution
4) 2
5) Chadwick
6) Protons and neutrons
7) 10-13 cm
8) Similar chemical but different physical properties
9) (b)
10) (b)
11) (a)
12) (c)
13) (a)
14) (a)
15) (d)
16) (a)
17) mass of 1 atom = 126.023×1023=1.993×10−23gm.
18) The increasing order of effective nuclear charge (Zeff)
experienced by the electron present in them is s > p > d because s is
close to the nucleus, and it will shield the nuclear charge more
effectively.
19) This is due to the small size of the fluorine atom. As a result of
the strong interelectronic repulsions in fluorine’s relatively small 2p
orbitals, the incoming electron does not experience much attraction.
20) P is surrounded by 5 bond pairs and no lone pairs in PCl 5,
whereas iodine atom is surrounded by 5 bond pairs and one lone pair in
IF5, so the shape of PCl5 is trigonal bipyramidal and IF5 is square
pyramidal
21) Here, Cl2 is both oxidised and reduced in ClO– and Cl–,
respectively. Since Cl– cannot act as an oxidising agent (O.A.).
Therefore, Cl2 bleaches substances due to oxidising action of
hypochlorite ClO– ion.
22) The volumes of dinitrogen and dioxygen that combine (i.e., 45.4 L
and 22.7 L) have a simple ratio of 2: 1. As a result, it follows Gay
Lussac’s law of gaseous volumes.According to this law, “when gases
combine or are produced in a chemical reaction, they do so in a simple
volume ratio provided all gases are at the same temperature and
pressure.”
23) The four most important properties of p-block elements are as
follows:
(a) Both metals and nonmetals are present in p-block elements, but the
number of nonmetals is much greater than that of metals. Furthermore,
within a group, the metallic character increases from top to bottom,
while the non-metallic character increases from left to right along a
period in this block.
(b) Their ionisation enthalpies are higher than those of s-block
elements.
(c) They mostly combine to form covalent compounds.
(d) Some of them have compounds with multiple (variable) oxidation
states. In a period, their oxidising character increases from left to right,
while their reducing character increases from top to bottom.
24) In both water and dimethyl ether (CH3–O–CH3), oxygen atom is
central atom, and has the same hybridization, yet they have different
bond angles. Which one has a greater bond angle? Give reason.
25) The bond angle of dimethyl ether will be greater. More repulsion
will exist between bond pairs of CH3 groups attached in ether than
between bond pairs of hydrogen atoms attached to oxygen in the
water.
The carbon of CH3 in ether is attached to three hydrogen atoms via
bonds, and the electron pair of these bonds contribute to the electronic
charge density on the carbon atom. As a result, the repulsion between
two CH3 groups will be greater than that between two hydrogen atoms.
 26. None of the atoms’ O.N. changes in the first reaction. As a result, it
cannot be classified as a redox reaction. Because PbO is a basic oxide
that combines with HCl acid, it is an acid-base reaction.
PbO2 is reduced and functions as an oxidising agent in the second process, a
redox reaction.
27. PbO is a basic oxide, and it undergoes a straightforward acid-base reaction
with HNO3. In PbO2, on the other hand, lead is in the +4 oxidation state and
cannot be further oxidised. As a result, no reaction occurs. PbO 2 is thus inactive;
only PbO interacts with HNO3.
28. The uncertainty principle is only significantly applicable for the microscopic
particles, not macroscopic particles. That concluded from the measurement of
uncertainty:

For example, if we take the particle or an object of mass 1 milligram that is 10-
6 kg

We calculate the following,

∆x. ∆ν = 60626*10-34/ 4*3.14*10-6

= 10-28 m-2 s -1

29. a) there will be 9 orbitals.

b) (i) The shape will be lobed , total electrons will be 6
(ii) The shape will be spherical, total electrons will be 2
c) There will be 2 electrons in each shell with opposite spin
d) s orbital : spherical shape
p orbital : lobed shaped
e) two d-orbitals that are on-axis. will be Dz^2 and Dx^2-Dy^2
30. covalent bond
ionic bond
chemical bond
chemical compound
31. P1 = 1atm, P2 = ½ = 0.5 atm, T1 = 273.15, V2 = ?, V1 = ?
32 g of dioxygen occupies = 22.4 L volume at STP
∴ 1.6 g of dioxygen will occupy =
22.4×1.632=1.12

V1 = 1.12 L
From Boyle’s law (as T is constant)

P1 V 1 = P 2V 2
2=1×1.120.6=2.24

V2 = 22.4 L
(ii) Number of moles of dioxygen = Mass of dioxygen/Molar mass of
dioxygen
=1.63.2=0.05

1 mol of dioxygen = 6.022 × 1023 molecule of dioxygen

∴ 0.05 mol of dioxygen = 6.022 × 1023 × 0.5 molecules of dioxygen
= 0.3011 × 1023 molecules
= 3.011 × 1022 molecules.
32. A modification to the Bohr model was required due to certain defects. The
Bohr model is applied to atoms with a single electron. It cannot account for
multi-electron atoms. It also claims that electrons move in circular orbits around
the nucleus, which is incorrect.
The dual behaviour of matter and the Heisenberg uncertainty principle were
two significant developments that contributed significantly to the formulation
of such a model.
In 1972, Werner Heisenberg, a German physicist, stated the uncertainty
principle, which is the result of the dual behaviour of matter and radiation. The
existence of definite paths or trajectories of electrons and other similar particles
is governed by the Heisenberg Uncertainty Principle, which is one of its most
important implications.
Quantum mechanics is a theoretical science that studies the motions of
microscopic objects that have both observable wave and particle properties.
The new atom model is known as the Quantum Mechanical Model of Atom.

33. Disproportionation is a redox reaction in which one intermediate oxidation

state component transforms into two higher and lower oxidation state
compounds.
The element must be in at least three oxidation states for such a redox reaction
to occur. As a result, that element is in the intermediate state during the
disproportionation reaction and can transition to both higher and lower
oxidation states.
Fluorine is the most electronegative and oxidising element of all the halogens,
and it is also the smallest.
It doesn’t have a positive oxidation state (only one) and doesn’t go through the
disproportionation reaction.