UPSC Prelims 2002 · General Studies
Question 110: Science and Technology
Match List I (Oxidation number) with List II (The element) and select the correct answer using the codes given below the lists: List I (Oxidation number) — List II (The element) A. 2 — 1. Oxidation number of Mn in MnO₂ B. 3 — 2. Oxidation number of S in H₂S₂O₇ C. 4 — 3. Oxidation number of Ca in CaO₂ D. 6 — 4. Oxidation number of Al in NaAlH₄
AnswerThe answer is (a).
Calcium in calcium peroxide (CaO2) is +2, because the peroxide group carries -2 in all (A-3). In NaAlH4, with sodium +1 and hydrogen as hydride -1, aluminium is +3 (B-4). Manganese in MnO2 is +4 (C-1). Sulphur in H2S2O7 is +6, since 2 + 2x - 14 = 0 (D-2). So A-3, B-4, C-1, D-2.
- A. Oxidation number 2 matches 3, Ca in CaO2.
- B. Oxidation number 3 matches 4, Al in NaAlH4.
- C. Oxidation number 4 matches 1, Mn in MnO2.
- D. Oxidation number 6 matches 2, S in H2S2O7.
Why each option is right or wrong
- (a) Right: A-3, B-4, C-1, D-2.
- (b) C and D are right, but A and B are swapped.
- (c) A and B are right, but C and D are swapped.
- (d) All four pairs are mismatched.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2002, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.