Oxidation involves loss of electrons Steps:

• Define oxidation as loss of electrons in a redox reaction.
• Examine each option for the substance oxidized and supporting evidence.
• Verify evidence matches electron transfer or oxidation state change.
• Identify the option with accurate identification and evidence.

Why B is correct:

• Sodium is oxidized from Na(0) to Na+(+1), losing one electron per atom, as per the definition of oxidation in redox reactions.

Why the others are wrong:

• A: CuO is reduced (Cu gains electrons); "this oxide has" provides no valid oxidation evidence.
• C: Nitrogen is reduced (gains electrons, oxidation state 0 to -3); it did not lose an electron.
• D: Zinc is reduced (gains two electrons); evidence incorrectly attributes gain to zinc instead of Mg's loss.

Final answer: B