CBSE CLASS 11 CHEMISTRY Examination 2025-26
XI – CHEMISTRY
Time: 3:00 hours
MM: 70
1. Multiple choice questions carrying 1 mark each.
1. What will be the molality of the solution containing 18.25 g of HCl gas in 500 g of water?
(a) 0.1 m
(b) 1 m
(c) 0.5 m
(d) 0.2 m
2. Azimuthal quantum number defines:
(a) e/m ratio of electron
(b) spin of electron
(c) angular momentum of electron
(d) magnetic momentum of electron
3. The group number, number of valence electrons, and valency of an element with the atomic number 15, respectively, are:
(a) 16, 5 and 2
(b) 15, 5 and 3
(c) 16, 6 and 3
(d) 15, 6 and 2
4. According to VSEPR theory, which of the following molecules has a seesaw shape?
(a) CH4
(b) SF4
(c) XeF4
(d) PCl5
5. During the process of conversion of ice into the water the specific heat capacity is given by______
(a) Zero
(b) positive
(c) infinity
(d) negative
6. In the P³⁻, S²⁻, and Cl⁻ ions, the increasing order of size is:
(a) Cl⁻, S²⁻, P³⁻
(b) P³⁻, Cl⁻, S²⁻
(c) S²⁻, Cl⁻, P³⁻
(d) S²⁻, P³⁻, Cl⁻
7. The oxidation number of an atom in the elemental state is:
(a) -1
(b) 0
(c) 1
(d) 2
8. The I.U.P.A.C. name of the given compound is
(a) 3–Methyl cyclohexene
(b) 1–methyl cyclohex–2–ene
(c) 6–methyl cyclohexene
(d) 1–methyl cyclohex5–ene
9. Find the correct order for the ease of formation of free radicals
(a) 1° > 2° > 3°
(b) 3° > 2° > 1°
(c) 2° > 1° > 3°
(d) 2° > 3° > 1°
10. The hybridisation of C involved in acetylene is:
(a) Sp²
(b) Sp³
(c) Sp
(d) dsp³
11. Acidic hydrogen is present in
(a) Ethyne
(b) Ethene
(c) Benzene
(d) Ethane
12. One mole of oxygen gas at STP is equal to _____.
(a) 6.022 × 10²² molecules
(b) 6.022 × 10²³ atoms of oxygen
(c) 16 g of oxygen
(d) 32 g of oxygen
Directions :
Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer. You have to select one of the codes (a), (b), (c) and (d) given below.
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion.
(c) Assertion is correct, reason is incorrect.
(d) Assertion is incorrect, reason is correct.
13. Assertion A: F atom has less negative electron gain enthalpy than Cl atom.
Reason R: Additional electrons are repelled more effectively by 3p-electrons in Cl than by 2p-electrons in F atom.
14. Assertion A: At critical point, the densities of gaseous and liquid state become same.
Reason R: At critical point, gases behave ideally.
15. Assertion A: The empirical mass of ethene is half of its molecular mass.
Reason R: The empirical formula represents the simplest whole number ratio of various atoms present in a compound.
SECTION-B
This section contains 7 questions with internal choice in one question. The following questions are very short answer type and carry 2 marks each.
1. Explain, why (CH₃)₃–C⁺ is more stable than CH₃–CH₂⁺ and CH₃⁺ is the least stable cations.
2. Use molecular orbital theory to explain why the Be₂ molecule does not exist.
3. A sugar syrup of weight 214.2 g contains 34.2 g of sugar (C₁₂H₂₂O₁₁). Calculate
(i) molal concentration, and
(ii) mole fraction of sugar in the syrup
4. At 500 K, equilibrium constant, Kc, for the following reaction is 5.
½ H₂(g) + ½ I₂(g) ⇌ HI(g)
What would be the equilibrium constant Kc for the reaction?
2HI(g) ⇌ H₂(g) + I₂(g)
5. What is ionization enthalpy? What are the various factors due to which the ionization enthalpy of the main group elements tends to decrease down a group?
6. Calculate ΔU, q and w when 2.0 mol of an ideal gas at 25°C are compressed isothermally and reversibly from 1.0 bar to 10.0 bar.
7. Predict whether the following molecules are aromatic or not?
(a) Cyclobutadiene
(b) Cyclopentadienyl anion
Or
Write the IUPAC names for the following compounds:
(a) CH₃–CH(CH₃)–CH₂–CHO
(b) CH₃–CH(CH₃)CH=CH–COOH
PART – 3
SECTION-C
This section contains 7 questions with internal choice in one question. The following questions are short answer type and carry 3 marks each.
1. (a) Name the chain isomers of C₅H₁₂ which has a tertiary hydrogen atom.
(b) How many isomers are possible for disubstituted benzene?
(c) Write the name of isomerism of the following compounds:
CH₃–O–CH₂CH₂CH₃ and C₂H₅–O–C₂H₅
2. (a) Define Fajans' Rule. Explain this effect of size of cation and anion on covalent character with examples.
(b) Explain why AlCl₃ is more covalent than NaCl.
3. (a) State Hess's law of constant heat summation.
(b) For the reaction at 298K
2A(g) + B(g) → 2D(g)
ΔU° = −10.5 kJ and ΔS° = −44.1 JK⁻¹
Calculate ΔG° for the reaction and predict whether the reaction may occur spontaneously.
Or
The solubility product of AgCl is 1.6 × 10⁻¹⁰. Calculate:
(i) The solubility of AgCl in water.
(ii) The degree of dissociation (α) of AgCl in its saturated solution.
4. A compound contains 4.07% hydrogen, 24.27% carbon and 71.65% chlorine. Its molecular mass is 98.96. What are its empirical and molecular formulae?
5. (i) An atomic orbital has n = 3. What are the possible values of l and mₗ?
(ii) How many electrons in an atom can have n + l = 4?
(iii) Calculate the total number of angular nodes and radial nodes present in 3p orbital.
6. Write the name of the reaction and the product formed in each case:
(i) 2CH₃Cl + 2Na —dry ether→ ?
(ii) C₆H₅N₂⁺Cl⁻ —CuCl→ ?
(iii) C₆H₅OH + CHCl₃ + NaOH → ?
7. Balance the net ionic equation for the following reaction in acidic solution by oxidation number method.
Mg(s) + VO₄³⁻(aq) → Mg²⁺(aq) + V²⁺(aq)
PART – 4
SECTION-D
Case based question carrying 5 marks
Due to the maximum percentage of s character (50%), the sp hybridised orbitals of carbon atoms in ethyne molecules have highest electronegativity; hence, these attract the shared electron pair of the C-H bond of ethyne to a greater extent than that of the sp² hybridised orbitals of carbon in ethene and the sp³ hybridised orbital of carbon in ethane. Thus, in ethyne, hydrogen atoms can be liberated as protons more easily as compared to ethene and ethane. Hence, hydrogen atoms of ethyne attached to triply bonded carbon atom are acidic in nature.
i) Among the following, the strongest acid is.
a) HC≡CH
b) C₆H₆
c) C₂H₆
d) CH₃OH
ii) Account for the decreasing order of acidity: ethyne, benzene, hexane
iii) Compare the melting point and boiling point of alkynes, alkene and alkanes. Write the reason for the difference.
iv) Alkynes contain two pi bonds but does not show geometrical isomerism. Why?
v) Which has maximum electronegativity among sp, sp², sp³ carbon?
SECTION-E
The following questions are long answer type and carry 5 marks each. One question has an internal choice.
1. (a) What is Zeeman effect and Stark effect?
(b) Calculate the energy associated with the first orbit of He⁺. What is the radius of this orbit?
Or
(a) State the Heisenberg's Uncertainty Principle.
(b) Write the mathematical equation of Heisenberg's Uncertainty Principle.
(c) Why electron cannot exist inside the nucleus according to Heisenberg's uncertainty principle?
2. (i) What happens when (write equations only)
(a) Propene is treated with bromine water.
(b) Butyne is treated with sodium in liquid ammonia.
(c) sec-Butylbromide is treated with alcoholic KOH.
(ii) An alkene C₄H₈ upon ozonolysis gives 2 moles of formaldehyde and 1 mole of glyoxal. What is the name of alkene?
3. (a) Derive ΔH = ΔU + Δn₉RT
(b) The reaction of cyanamide NH₂CN, with dioxygen was carried out in a bomb calorimeter and ΔU was found to be −742.7 kJ mol⁻¹ at 298K. Calculate the enthalpy change of the reaction at 298K.
NH₂CN(s) + 3/2 O₂(g) → N₂(g) + CO₂(g) + H₂O(l)
