Chemistry · Class 11 Science

West Bengal Wbchse Class 11 Chemistry — Real Previous-Year Papers

with complete answers

Real previous-year board papers, year by year — the official exam pattern, the full question paper, and every question solved the concept-first way. Distinct from the chapter-wise textbook bank.

2018–2018
Years of papers: 1
Total Papers: 1
Real Board Papers: 0
Sample papers: 35
Real-paper Q & A: 0
Sample-paper Q & A

Real board-paper questions available, by year

35 Q2018complete

West Bengal HS First Year (WBCHSE Class XI) Annual Examination 2018 · Set ANNUAL

Real board examination

This paper has 27 questions on a topic removed in CBSE’s 2023-24 syllabus update (each marked Not in syllabus). It’s kept for historical accuracy — the exam really asked it that year — but isn’t in the current syllabus and doesn’t count toward a concept’s importance. Switch to to focus on what’s still examinable.

About this paper

The real Class-12 board examination held in 2018. Every question below is solved the concept-first way. Sample papers are labelled honestly — never shown as a past exam.

Total marks: —
Questions: —
Duration: —
Sections: —

The marks / questions / duration above are the official exam pattern. We currently have 35 of this paper’s questions, with 35 fully solved. Questions we couldn’t yet extract or verify are held — never shown as complete.

The question paper

The questions we hold for this paper, laid out by section. Solutions are on the Answers tab.

Board Examination

Chemistry

West Bengal HS First Year (WBCHSE Class XI) Annual Examination 2018 · Set ANNUAL

Series/Set: ANNUALRoll No. ________

Time Allowed: —Maximum Marks: —

Section A

Q1.

Which of the following is the ground state electronic configuration of Cr? (Atomic number of Cr is 24)

(a) 1s²2s²2p⁶3s²3p⁶3d⁴4s²
(b) 1s²2s²2p⁶3s²3p⁶3d⁵4s¹
(c) 1s²2s²2p⁶3s²3p⁶3d⁶
(d) 1s²2s²2p⁶3s²3p⁶3d³4s²4p¹

[1]

Q2.

The state of hybridisation of the central atom of which of the following is sp³d²?

(a) SF₄
(b) PCl₅
(c) SF₆
(d) SO₄²⁻

[1]

Q3.

Which of the following is the correct order of repulsive interaction of lone pair (lp) and bond pair (bp) of electrons?

(a) lp–lp > lp–bp > bp–bp
(b) lp–bp > lp–lp > bp–bp
(c) bp–bp > lp–lp > lp–bp
(d) lp–lp > bp–bp > lp–bp

⚠ This question is not in the current syllabus

[1]

Q4.

The cause of spherical shape of water drops is

(a) viscosity
(b) surface tension
(c) hydrogen bond
(d) high critical temperature of H₂O vapour

[1]

Q5.

An amount of work w is done by a system and q amount of heat is supplied to the system. By which of the following relations the change in internal energy of the system can be expressed?

(a) ΔU = q − w
(b) ΔU = q + w
(c) ΔU = q
(d) ΔU = w − q

⚠ This question is not in the current syllabus

[1]

Q6.

Which one of the following indicates a spontaneous process?

(a) ΔG = 0
(b) ΔH = TΔS
(c) ΔG > 0
(d) ΔG < 0

⚠ This question is not in the current syllabus

[1]

Page 1 of 6

Q7.

The relation between Kp and Kc for the following reaction: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) is (a) Kp = Kc (b) Kp = Kc(RT)⁻¹ (c) Kp = KcRT (d) Kp = Kc(RT)²

⚠ This question is not in the current syllabus

[1]

Q8.

Which one of the following elements shows diagonal relationship with magnesium? (a) Na (b) Li (c) Be (d) Ca

⚠ This question is not in the current syllabus

[1]

Q9.

Sodium is preserved in which of the following liquids? (a) Water (b) Ethanol (c) Kerosene oil (d) Methanol

⚠ This question is not in the current syllabus

[1]

Q10.

Which of the following is a carbanion? (a) CH₃O⁻ (b) CH₃CH₂⁻ (c) CH₃COO⁻ (d) C₆H₅O⁻

⚠ This question is not in the current syllabus

[1]

Q11.

In the Lassaigne test for the detection of nitrogen in an organic compound, with which of the following metals the organic compound is fused? (a) Li (b) Mg (c) Na (d) Zn

⚠ This question is not in the current syllabus

[1]

Q12.

Which of the following compounds does not produce a white precipitate on treatment with ammoniacal silver nitrate solution? (a) Acetylene (b) Methyl acetylaene (c) Ethyl acetylene (d) Dimethyl acetylene

⚠ This question is not in the current syllabus

[1]

Q13.

In which of the following reactions the product is not formed according to Markownikoff's rule? (a) CH₃CH=CH₂ + HCl → (b) CH₃CH=CH₂ + HCl —(Peroxide)→ (c) CH₃CH=CH₂ + HBr → (d) CH₃CH=CH₂ + HBr —(Peroxide)→

⚠ This question is not in the current syllabus

[1]

Q14.

Which of the following gases emitted by motor vehicles is responsible for the formation of photochemical smog? (a) SO₂ (b) CO (c) NO (d) CO₂

⚠ This question is not in the current syllabus

[1]

Section B

Q1.

The empirical formula of an organic compound is CH₂O and its molecular weight is 180. What is the molecular formula of the compound? (H = 1, C = 12, O = 16)

[1]

Page 2 of 6

Q2.

Arrange the following elements in the increasing order of their first ionisation enthalpy: Li, Be, Na, Mg **OR** Arrange the following elements in the decreasing order of their electronegativity: Si, N, F, Cl

⚠ This question is not in the current syllabus

[1]

Q3.

What is meant by an isolated system in thermodynamics? **OR** Write the SI unit of entropy.

⚠ This question is not in the current syllabus

[1]

Q4.

What reagent can be used for the following conversion? HC≡CH → H₂C=CH₂

⚠ This question is not in the current syllabus

[1]

Q5.

How many neutrons are present in 5×10⁻⁴ moles of ¹⁴₆C? **OR** Determine the mass percentage composition of water (H = 1, O = 16).

⚠ This question is not in the current syllabus

[2]

Q6.

State Heisenberg uncertainty principle. What is the shape of s orbital?

⚠ This question is not in the current syllabus

[2]

Q7.

Explain why SiCl₄ undergoes hydrolysis readily. **OR** Why is aqueous solution of borax alkaline?

⚠ This question is not in the current syllabus

[2]

Q8.

Which reagent is called an electrophile in organic reaction? Write with an example. **OR** Write the IUPAC names of the compounds CH₂=CHCH₂CH₂C≡CH and CH₃CH=CHCH₂C≡CH.

⚠ This question is not in the current syllabus

[2]

Q9.

Mention two causes of soil pollution. **OR** How does the increase in the amount of CO₂ in the atmosphere lead to global warming?

⚠ This question is not in the current syllabus

[2]

Page 3 of 6

Section C

Q1.

(i) Write with an example the condition for two atoms to be considered as isobars. (ii) Why is Fe³⁺ more stable than Fe²⁺? [2 + 1] **OR** (i) What are the quantum numbers by which an electron in an atom can be designated? (ii) What is the maximum number of quantum numbers that may be the same for two electrons of an atom? [2 + 1]

[3]

Q2.

(i) The outermost electronic configuration of the atom of an element is 3s²3p³. Mention the position of the element in the long periodic table. (ii) Why is electron gain enthalpy of oxygen less than that of sulphur? [1 + 2]

[3]

Q3.

Show by drawing its molecular orbital diagram why O₂ is paramagnetic. **OR** (i) Draw the canonicals of CO₃²⁻. (ii) Why is boiling point of H₂O greater than that of H₂S? [2 + 1]

⚠ This question is not in the current syllabus

[3]

Q4.

State Gay Lussac's law related to pressure and temperature of a gas. 3.2 g of sulphur when vaporised the sulphur vapour occupies a volume of 280.2 mL at STP. Determine the molecular formula of sulphur vapour under this condition. (S = 32) [1 + 2] **OR** Determine the volume of 2.2 g of carbon dioxide at 27°C and 570 mm Hg pressure.

⚠ This question is not in the current syllabus

[3]

Q5.

(i) State Hess's law. (ii) For the following reaction at 298 K: 2X + Y → Z, ΔH = 300 kJ mol⁻¹ and ΔS = 0.2 kJ K⁻¹ mol⁻¹. At what temperature will the reaction become spontaneous, considering ΔH and ΔS to be constant over the temperature range? [1 + 2]

⚠ This question is not in the current syllabus

[3]

Q6.

(i) What is the oxidation number of Mn in K₂MnO₄? (ii) Balance the following chemical equation by ion-electron method: Cr₂O₇²⁻ + Fe²⁺ + H⁺ → Cr³⁺ + Fe³⁺ + H₂O [1 + 2] **OR** (i) Balance the following chemical equation by oxidation number method: NaNO₃ + Zn + NaOH → NH₃ + Na₂ZnO₂ + H₂O (ii) What is the oxidation number of S in S₈? [2 + 1]

[3]

Page 4 of 6

Q7.

(i) What is heavy water? (ii) With balanced chemical equation, give an example of reducing property of H₂O₂. [1 + 2]

⚠ This question is not in the current syllabus — Asked in the 2018 WBCHSE Class-XI annual paper; the Hydrogen unit is not in the current WBCHSE Class-XI syllabus.

[3]

Q8.

Write the principle, with balanced chemical equations, of preparation of sodium carbonate by Solvay process.

⚠ This question is not in the current syllabus

[3]

Q9.

Show two canonicals of benzene by drawing. Benzene is stored in a bottle. Is there existence of the two canonicals in the benzene of the bottle? Answer with reason. [2 + 1] **OR** Between (CH₃)₃C–Cl and CH₃–Cl, which compound undergoes heterolytic fission readily in water? Why? [1 + 2]

⚠ This question is not in the current syllabus

[3]

Section D

Q1.

(i) State the law of mass action. (ii) What is a buffer solution? Give an example of an acidic buffer solution. (iii) If the concentrations of ammonia and ammonium chloride in a buffer solution of ammonia–ammonium chloride are 0.2 M and 0.3 M respectively, determine the pH of the buffer solution. (Given Kb(NH₃) = 1.76×10⁻⁵) [1 + 2 + 2] **OR** (i) Determine the pH of 0.1 M acetic acid solution. (pKa of acetic acid is 4.75) Is there any OH⁻ ion present in this solution of acetic acid? Answer with reason. (ii) Why does the rate of dissociation of H₂S in aqueous solution decrease in the presence of HCl? [3 + 2]

⚠ This question is not in the current syllabus

[5]

Q2.

(i) Why is carbon monoxide toxic? (ii) Write with balanced chemical equation what happens when aluminium is heated with concentrated aqueous solution of caustic potash. (iii) Write one use of each of Silicones and Zeolite. [1 + 2 + 2]

⚠ This question is not in the current syllabus

[5]

Page 5 of 6

Q3.

(i) Two isomeric compounds A and B having the molecular formula C₃H₇Br form the same compound C on dehydrobromination. C on ozonolysis produces acetaldehyde and formaldehyde. Identify A, B and C. (ii) How would you convert? (a) CH₂=CH₂ → HC≡CH (b) Benzene → Chlorobenzene (shown in the original paper) [3 + 2] **OR** (i) Write the mechanism of the following reaction: CH₄ + Cl₂ —(Diffused sunlight)→ CH₃Cl + HCl (ii) How would you convert? (a) Benzene → Acetophenone (shown in the original paper) (b) Benzene → Benzenesulfonic acid (shown in the original paper) (c) CH₂=CH₂ → CH₃CH₂OH [2 + 3]

[5]

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