SSLC Chemistry Second Term Exam 2025 – Answer Key

Subject: Chemistry | Standard: X | Total Score: 40 | Time: 1½ Hours

Note: This answer key provides the correct responses based on standard Chemistry knowledge. For questions with choices, only one selected answer is provided per the instruction.

Section 1: Questions 1 to 4 (Each 1 score)

1 score

1. The products of electrolysis of aqueous NaCl are:

C. H₂, Cl₂ and NaOH

In aqueous NaCl electrolysis, H⁺ from water is reduced at cathode to H₂, Cl⁻ is oxidized at anode to Cl₂, and NaOH remains in solution.

1 score

2. Two statements are given:

B. Statement 1 is correct but statement 2 is not correct.

Octyl ethanoate smells like pineapple, but it is prepared from octanol and ethanoic acid, not ethanol and octanoic acid.

1 score

3. Match the following:

C. (a)-(iv), (b)-(iii), (c)-(i)

17 g NH₃ = 1 mole = 6.022×10²³ molecules; 88 g CO₂ at STP = 2 moles = 44.8 L; 14 g N = 0.5 mole N atoms = 3.011×10²³ atoms ≈ 6.022×10²³ atoms per mole basis match.

1 score

4. Assertion (A) and Reason (R):

B. A is correct, but R is not correct.

The last electron of d-block in 4th period goes to 3d (penultimate shell). However, 3d has higher energy than 4s only before filling; after filling, 3d is lower. R is incorrect in general.

Section 2: Questions 5 to 11 (Each 2 scores, with choice)

2 scores

5. Write the structural formulae of:

a. Pentanal: CH₃CH₂CH₂CH₂CHO

b. Pent-2-yne: CH₃C≡CCH₂CH₃

2 scores

6. Two statements regarding a block of elements:

a. f-block elements

b. They are radioactive / show +3 oxidation state / form colored ions / are paramagnetic.

2 scores

7. (A) Orbitals with (n+l)=5:

a. 3d (5 orientations) and 4p (3 orientations)

b. 4p has higher energy because higher n value.

2 scores

8. Fuel cell:

a. A cell that converts chemical energy of fuel directly into electrical energy.

b. Advantage: High efficiency / no pollution / continuous operation.

2 scores

9. (A) Saturated organic compound with 4C and -OH:

a. Butan-1-ol (CH₃CH₂CH₂CH₂OH) and Butan-2-ol (CH₃CH₂CH(OH)CH₃)

b. Functional isomer: Ethoxyethane (C₂H₅OC₂H₅) or methoxypropane, etc.

2 scores

10. Cu rod in AgNO₃ solution:

a. Solution turns blue.

b. Copper is oxidized.

2 scores

11. Qualities of a mineral used as ore:

1. High metal content
2. Easy extraction
3. Low impurities
4. Economical to mine
5. Readily available

Section 3: Questions 12 to 17 (Each 3 scores, with choice)

3 scores

12. (A) Starting from ethyne:

a. Ethene: H₂ addition with Pd catalyst
b. Polythene: Polymerization of ethene
c. Chloroethane: Add HCl to ethene

3 scores

13. Gas volume problem:

a. Using V₁/T₁ = V₂/T₂, V₂ = 7.27 L ≈ 7.3 L

b. Charles’s Law

3 scores

14. Metal M in Period 4, Group 11:

a. [Ar] 3d¹⁰ 4s¹

b. M⁺: [Ar] 3d¹⁰; M²⁺: [Ar] 3d⁹

3 scores

15. Subshell configurations:

a. A and C belong to same period? None; A is period 3, C is period 2.

b. B: Period 4, Group 7

c. Same group as A: Any noble gas configuration element (e.g., Ne, Ar)

3 scores

16. (A) Galvanic cells:

a. Mg-Cu gives higher voltage (greater E⁰ difference).

b. Electrons flow from Mg to Cu.

c. Zn → Zn²⁺ + 2e⁻

3 scores

17. Graphs and Avogadro’s Law:

a. Graph showing V ∝ n (straight line through origin)

b. Equal volumes of gases at same T and P contain equal number of molecules.

c. V₂ = (5/20)×640 = 160 L

Section 4: Question 18 (4 scores, with choice)

4 scores

18. (A) CO₂ calculations:

a. Molar mass = 12 + 32 = 44 g/mol

b. 880 g CO₂ = 20 moles, Volume = 20 × 22.4 = 448 L

c. 440 g CO₂ = 10 moles, Molecules = 10 × 6.022×10²³ = 6.022×10²⁴

d. C + O₂ → CO₂, 12 g C gives 44 g CO₂, so for 88 g CO₂, mass of C = 24 g

End of Answer Key – This key is prepared based on standard academic references. For any discrepancies, consult your subject teacher.