Question

What are the oxidation numbers of the atoms in this reaction?

Check all that apply.

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

0 for Mg in Mg and MgCl2

0 for Mg(s) and H in H2

+1 for H in HCl

-1 for Cl in HCl

+2 for Mg in MgCl2

Answer 1

The true statements are the last four; the first is false.

Correct:
- 0 for Mg(s) and H in H2 — both are elemental, oxidation number 0.
- +1 for H in HCl — hydrogen in HCl is +1.
- -1 for Cl in HCl — chlorine in HCl is -1.
- +2 for Mg in MgCl2 — Mg must be +2 to balance two Cl−.

Incorrect:
- 0 for Mg in Mg and MgCl2 — Mg in MgCl2 is +2, not 0.