Correct Option
The correct matching is A-3, B-4, C-1, D-2.
- A. Oxidation number of Ca in CaO: Calcium (Ca) is an alkaline earth metal, which typically exhibits an oxidation number of +2 in its compounds. In CaO, assuming oxygen has an oxidation number of -2, the oxidation number of Ca is calculated as Ca + (-2) = 0, thus Ca = +2. Therefore, 2 matches with 3.
- B. Oxidation number of Al in NaAlH₄: In sodium aluminium hydride, sodium (Na) has an oxidation number of +1, and hydrogen (H) as a hydride has an oxidation number of -1. For the compound to be neutral, the sum of oxidation numbers must be zero: (+1) + Al + 4(-1) = 0. This calculation yields Al - 3 = 0, so Al = +3. Therefore, 3 matches with 4.
- C. Oxidation number of Mn in MnO₂: In manganese dioxide, oxygen (O) typically has an oxidation number of -2. For the compound to be neutral, the sum of oxidation numbers must be zero: Mn + 2(-2) = 0. This calculation yields Mn - 4 = 0, so Mn = +4. Therefore, 4 matches with 1.
- D. Oxidation number of S in H₂S₂O₇: In pyrosulfuric acid (H₂S₂O₇), hydrogen (H) has an oxidation number of +1, and oxygen (O) has an oxidation number of -2. For the compound to be neutral, the sum of oxidation numbers must be zero: 2(+1) + 2S + 7(-2) = 0. This calculation yields 2 + 2S - 14 = 0, so 2S = 12, and S = +6. Therefore, 6 matches with 2.
Incorrect Options
Options 2, 3, and 4 are incorrect as they do not provide the accurate assignment of oxidation numbers to the respective elements in the given compounds, based on standard rules for calculating oxidation states.