In the reaction 2H$_2$S + SO$_2$ $\longrightarrow$ 3S$\downarrow$ + 2H$_2$O, which reactant acts as the oxidant?
ASO$_2$
BH$_2$S
CH$_2$O
DS
Answer & Solution
Correct answer: A. SO$_2$
1. H$_2$S loses hydrogen (forming H$_2$O and S), so H$_2$S is oxidised and acts as the reductant.
2. The oxidant is the species that causes this oxidation while being reduced itself.
3. SO$_2$ loses oxygen (it becomes S), i.e. it is reduced, so SO$_2$ is the oxidant.
4. S and H$_2$O are products, not the reacting agents, and H$_2$S is the reductant, not the oxidant, so those options are wrong.
_Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 3 "Chemical Reactions and Equations", p.52_
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