CBSE Class 11 Chemistry Pre-Final Examination Question Paper 2025-26: St. Margaret School, Rohini

School Name:	St. Margaret Sr. Sec. School, Prashant Vihar, Sector 14, Rohini, New Delhi – 110085, India
Class:	11th Standard (CBSE)
Subject:	Chemistry
Time Duration:	3 Hours
Maximum Marks:	70
Examination:	Pre-Final Examination (2025–26)

GENERAL INSTRUCTIONS

Read the following instructions carefully.
There are 33 questions in this question paper with internal choice.
SECTION A consists of 16 multiple-choice questions carrying 1 mark each.
SECTION B consists of 5 very short answer questions carrying 2 marks each.
SECTION C consists of 7 short answer questions carrying 3 marks each.
SECTION D consists of 2 case-based questions carrying 4 marks each.
SECTION E consists of 3 long answer questions carrying 5 marks each.
All questions are compulsory.
Use of log tables and calculators is not allowed.

SECTION – A

(1 Mark Each)

Question 01: The number of significant figures in 0.001620 are:

1. 4
2. 3
3. 6
4. 2

Question 02: Which of the following pairs of d-orbitals have electron density along the axis?

1. d_xz, d_yz
2. d_xy, d_yz
3. d_z², d_x²−y²
4. d_xy, d_x²−y²

Question 03: If the initial concentrations of reactants in a reaction increase then the equilibrium constant:

1. Also increases
2. Decreases
3. Remains constant
4. May increase or decrease

Question 04: The oxidation number of Cr in K₂Cr₂O₇ is:

1. −6
2. +6
3. +2
4. −2

Question 05: The structure of 4-Methylpent-2-en-1-ol is:

1. CH₃CH₂CH=CHCH₂OH
2. (CH₃)₂C=CHCH₂CH₂OH
3. (CH₃)₂CHCH=CHCH₂OH
4. CH₃CH(OH)CH–CH=C(CH₃)₂

Question 06: Which of the following molecules have trigonal planar geometry?

1. BF₃
2. NH₃
3. PCl₃
4. IF₃

Question 07: Which of the following electronic configurations of an atom has the lowest ionisation enthalpy?

1. 1s² 2s² 2p³
2. 1s² 2s² 2p⁶ 3s¹
3. 1s² 2s² 2p⁵
4. 1s² 2s² 2p⁶

Question 08: Compare the given compounds and select the one in which nitrogen can be estimated by Kjeldahl’s method.

1. Azo compounds
2. Nitrobenzene
3. Pyridine
4. Benzylamine

Question 09: Choose the correct statement related to formation of Nitronium ion as an electrophile:

1. Sulphuric acid acts as an acid and nitric acid acts as a base.
2. Sulphuric acid acts as a base and nitric acid acts as an acid.
3. Sulphuric acid and nitric acid both act as acids.
4. HSO₄⁻ acts as conjugate acid and H₂NO₃⁺ acts as conjugate base.

Question 10: For the reversible reaction
N₂(g) + 3H₂(g) ⇌ 2NH₃(g) + Heat
The equilibrium shifts in forward direction:

1. By increasing the concentration of NH₃(g)
2. By decreasing the pressure
3. By decreasing the concentration of N₂ and H₂
4. By increasing pressure and decreasing temperature

Question 11: Identify the correct expression for internal energy change for an adiabatic process.

1. ΔU = 0
2. ΔU = −q
3. ΔU = W
4. ΔU = +q

Question 12: Which of the following compounds will exhibit cis-trans isomerism?

1. Butanol
2. 2-Butyne
3. 2-Butenol
4. 2-Butene

Question 13: Assertion (A): Methane cannot be obtained by Wurtz reaction.
Reason (R): Wurtz reaction leads to the formation of symmetrical alkane having an even number of carbon atoms.

Question 14: Assertion (A): Spontaneous process is an irreversible process and may be reversed by some external agency.
Reason (R): Decrease in enthalpy is a contributory factor for spontaneity.

Question 15: Assertion (A): For the reaction
2SO₂(g) + O₂(g) ⇌ 2SO₃(g); ΔH = −193.2 kJ
Increase in temperature favours the decomposition of SO₃.
Reason (R): Increase in temperature favours endothermic reactions.

Question 16: Assertion (A): The H–N–H bond angle in NH₃ is smaller than H–O–H bond angle in H₂O.
Reason (R): Nitrogen has one lone pair and oxygen has two lone pairs.

SECTION – B

(2 Marks Each)

Question 17: The density of 3 M solution of NaCl is 1.25 g mL⁻¹. Calculate the molality of the solution.

Question 18: Write the electronic configuration of element with atomic number 25 and assign the position to the given element in the periodic table.

SECTION – C

(3 Marks Each)

Question 19: Calculate the electron gain enthalpy of fluorine from the data given below:

ΔH° of KF = −560.8 kJ mol⁻¹
Sublimation energy of K = 87.8 kJ mol⁻¹
Dissociation energy of F₂ = 158.9 kJ mol⁻¹
Lattice energy of KF = −807.5 kJ mol⁻¹
Ionisation energy of K = 414.2 kJ mol⁻¹

Question 20: Balance the following redox reaction in acidic medium by ion-electron method:

Cr₂O₇²⁻ + 3SO₂ + 2H⁺ → ?

Question 21: Write the following reactions with examples:

1. Wurtz reaction
2. Markovnikov rule

Question 22: Calculate the standard enthalpy of formation of CH₃OH(l) from the following data:

i) CH₃OH(l) + 3/2 O₂(g) → CO₂(g) + 2H₂O(l)
ΔH° = −726 kJ mol⁻¹

ii) C(g) + O₂(g) → CO₂(g)
ΔH° = −393 kJ mol⁻¹

iii) H₂(g) + 1/2 O₂(g) → H₂O(l)
ΔH° = −286 kJ mol⁻¹

Question 23: Explain the following:

1. Mg has larger first ionisation enthalpy than Al.
2. The size of an anion is always larger than that of the parent atom.
3. Second electron gain enthalpy of oxygen is positive.

OR

Arrange the following according to the property mentioned in bracket:

1. N, O, F (increasing order of electron gain enthalpy)
2. N³⁻, O²⁻, F⁻ (increasing order of effective nuclear charge)
3. Group 17 elements (increasing order of reactivity)

Question 24:

1. Write down geometrical isomer of CHCl=CHCl.
2. Draw the eclipsed and staggered form of butane in Newman’s projection.
3. Complete the following reaction:
   CH₃CH=CH₂ + HBr (Peroxide) → ?

Question 25: Calculate the ΔH° for the reaction:

H₂(g) + Br₂(g) → 2HBr(g)

Bond enthalpies are given as:
H–H = 436 kJ mol⁻¹
Br–Br = 192 kJ mol⁻¹
H–Br = 368 kJ mol⁻¹

Question 26: Write IUPAC name of the following compounds (Any three).

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SECTION – D

(4 Marks)

Question 27: Calculate the oxidation number of sulphur, chromium and nitrogen in:

H₂SO₅, CrO₄²⁻ and NO₃⁻

Question 28:

1. Give reasons:
   1. Alkynes are acidic in nature (Give chemical equation to support your answer).
   2. Cyclopropene is not aromatic.
2. What happens when 2-bromobutane is treated with alcoholic KOH?

Question 29: Read the passage carefully and answer the questions that follow:

In our day-to-day life, we come across various mixtures of substances. Often in these mixtures the amount of one of the components is more than the other. To have a quantitative comparison, we express distribution of one substance into that of other by the term “concentration”. The concentration of a solution is expressed in many ways—molarity, molality, mole fraction, g/L, ppm, ppb and %. However, for pure substances, concentration term is meaningless; rather we talk about their percentage purity. Molarity is the number of moles of solute per litre of solution whereas molality is number of moles of solute per kilogram of solvent. Mole fraction is the ratio of moles of any component to the total moles of all components in the solution. Moreover, temperature-dependent terms are less preferred to express concentration.

1. Give two concentration terms which are independent of temperature. Give reason in support of your answer.
2. Mention the concentration term which is generally used to express composition of medicines in tablet form.
3. Calculate the molarity of pure water.

Question 30: Read the passage carefully and answer the questions that follow:

The process of rusting involves solid metal iron reacting with gaseous oxygen in presence of moisture to form solid hydrated ferric oxide. Going by phase change, it is obvious that randomness (entropy) is decreasing as gaseous oxygen is consumed and solid oxide is formed. This does not seem to support spontaneity. However, the process of rusting is a self-supporting reaction as the surplus energy generated in the reaction (−1648 kJ mol⁻¹) becomes dispersed to surroundings as heat and raises the entropy of the surroundings. On calculation, overall entropy (system + surroundings) ΔS_total is found to be positive (4.98 kJ mol⁻¹ K⁻¹), making the rusting reaction spontaneous.

1. Is rusting of iron feasible at all temperatures? Explain.
2. State second law of thermodynamics OR Define entropy.
3. Why is free energy a better criterion of spontaneity than entropy?

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SECTION – E

(5 Marks)

Question 31:

1. Discuss the shape of PCl₅ using VSEPR theory.
2. Draw the Lewis dot structure of NO₂.

OR

1. Explain the hybridisation of AlCl₄⁻.
2. Write hybridisation and shapes of:
   1. SF₄
   2. XeF₂
   3. CO₂
3. Give an example of polyatomic species having zero dipole moment.
4. What type of hydrogen bond is present in 2-hydroxybenzoic acid?

Question 32:

1. A 0.1 M solution of formic acid (HCOOH) has K_a = 4 × 10⁻⁵. Calculate:
   1. pH of the solution
   2. Percent dissociation of HCOOH
2. For the reaction:
   H₂(g) + Br₂(g) ⇌ 2HBr(g)
   The equilibrium amounts of H₂, Br₂ and HBr are 0.45 mol, 0.39 mol and 3 mol respectively at 25°C. Calculate K_c and K_p.

OR

The value of K_c for the reaction 2A ⇌ B + C is 2 × 10⁻⁴.
At a given time, [A] = [B] = [C] = 5 × 10⁻⁵ M.
Predict whether the reaction will favour formation of A. Justify your answer.

Give structure and IUPAC name of isobutyl alcohol.
The solubility of PbSO₄ in water is x. Calculate the solubility product constant of PbSO₄.

Question 33:

1. Write the structure for two functional isomers having the molecular formula C₄H₁₀O.
2. Give structure and IUPAC name for isobutyl alcohol.
3. For complete neutralisation of ammonia gas obtained from 2.8 g of inorganic compound, 20 millimoles of H₂SO₄ were required.
   Calculate the percentage of nitrogen in the sample.
   [Atomic masses: N = 14 u, S = 32 u, O = 16 u, H = 1 u]

OR

In the Carius method of estimation of sulphur, 0.2 g of organic compound contains 40% sulphur by mass.
Calculate the amount of BaSO₄ precipitate formed.
[Atomic masses: Ba = 137 u, S = 32 u, O = 16 u]

Explain +R and −R effect with examples.