alleryStart learning →What is the oxidation number of an atom in an elemental substance such as O2, Na or Cl2?
AIt equals plus one always
BIt equals minus one always
CIt equals zero in every case
DIt equals the group number
Answer & Solution
Correct answer: C. It equals zero in every case
1. The first guideline sets the oxidation number of any atom in an elemental substance at zero.
2. So Na(s), Cl2(g) and O2(g) all have atoms at zero.
3. This is the reference point that lets a change be spotted.
4. Sodium moving from 0 in Na to +1 in NaCl is therefore an increase, that is, oxidation.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 4 "Stoichiometry of Chemical Reactions", section 4.2 Classifying Chemical Reactions_
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