Answer;
A decomposition reaction in which a metal is reduced
Explanation;
A decomposition reaction occurs when one reactant breaks down into two or more products.This can be represented by the general equation: AB → A + B. Examples of decomposition reactions include the breakdown of hydrogen peroxide to water and oxygen, and the breakdown of water to hydrogen and oxygen.
During this reaction mercury oxide decomposes into mercury and oxygen. Mercury(II) oxide, a red solid, decomposes when heated to produce mercury and oxygen gas.