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What is the oxidation number of sulfur in H2S?
APlus two
BPlus four
CMinus two
DMinus four
Answer & Solution
Correct answer: C. Minus two
1. Hydrogen is bonded to a nonmetal here, so each H is +1.
2. Two hydrogen atoms contribute 2 times +1, which is +2.
3. H2S is a neutral molecule, so the oxidation numbers must sum to 0.
4. Therefore the sulfur value x satisfies 0 = (+2) + x, giving x = -2.
5. A positive answer would break the sum rule for a neutral molecule.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 4 "Stoichiometry of Chemical Reactions", section 4.2 Classifying Chemical Reactions_
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