Redox reactions involve electron transfer via oxidation state changes Steps:

• Identify redox by checking oxidation number changes in reactants/products.
• For A: Mg (0 to +2, oxidized), H (+1 to 0, reduced) → redox.
• For B: All elements retain states (K +1, C +4, O -2, H +1) → not redox.
• For C: Cu (+2), O (-2), H (+1), Cl (-1) unchanged → not redox.
• For D: Option missing, preventing analysis. Why D is correct:
• Not enough information; D's reaction undefined, so cannot confirm as redox despite statement. Why the others are wrong:
• A is redox due to oxidation state shifts.
• B is acid decomposition, no electron transfer.
• C is neutralization, no oxidation state changes.

Final answer: Not enough information.