Redox reactions involve electron transfer via oxidation state changes

Steps:

• Recall that redox reactions feature elements changing oxidation states: oxidation (loss of electrons) and reduction (gain).
• Assign oxidation numbers to reactants and products in each option.
• Check for any changes in oxidation numbers indicating electron transfer.
• Identify the option with clear oxidation and reduction half-reactions.

Why A is correct:

• Mg oxidizes from 0 to +2 (loses 2e⁻), while H reduces from +1 to 0 (gains 1e⁻ each), confirming electron transfer per the definition of redox.

Why the others are wrong:

• B: Acid-base decomposition; oxidation states unchanged (Mg +2, C +4 throughout).
• C: Neutralization; no oxidation state changes (Mg +2, O -2, H +1 constant).
• D: Neutralization; oxidation states remain the same (all elements retain original numbers).

Final answer: A