Assertion: In a reaction of zinc oxide with carbon, zinc oxide is reduced to zinc.Reason: In a chemical reaction, a substance is reduced when it gains oxygen.

The assertion is correct, but the reason is incorrect. In a reaction of zinc oxide with carbon, zinc oxide is indeed reduced to zinc. However, the reason is incorrect because in a chemical reaction, a substance is reduced when it loses oxygen, not gains. In this case, zinc oxide (ZnO) is reduced to zinc (Zn) by losing oxygen. The carbon (C) is oxidized to carbon monoxide (CO) by gaining the oxygen from the zinc oxide. This is an example of a redox reaction, where one substance is reduced (loses oxygen) and another is oxidized (gains oxygen).