Redox Reactions Involve Oxidation State Changes

Steps:

• Recall that redox reactions feature electron transfer, shown by changes in oxidation numbers.
• Equation 1: Mg rises from 0 to +2 (oxidized), H falls from +1 to 0 (reduced).
• Equation 2: Fe falls from +3 to +2 (reduced), Cl rises from -1 to 0 in NaCl₂ (oxidized).
• Equation 3: Na rises from 0 to +1 (oxidized), Br falls from 0 to -1 (reduced).

Why A is correct:

• All three equations exhibit oxidation number changes for at least two elements, meeting the redox definition.

Why the others are wrong:

• B omits equation 3, which is redox (Na oxidized, Br reduced).
• C omits equation 1, which is redox (Mg oxidized, H reduced).
• D omits equations 1 and 2, both redox (oxidation/reduction of Mg/H and Fe/Cl).

Final answer: A