If it goes down the number line, it is a reduction. Someone, in a fit of perversity, decided that we needed more description for the process. For the each word reaction, write the chemical equation without balancing it, write the oxidation state of each element above that element, and write the two half reactions, labeling which is oxidation and which is reduction. You can check your work by balancing the complete reaction using the numbers from the half reaction addition. Mercuric oxide, a red powder, is put into a test tube and warmed.
Potassium chlorate is heated in a test tube.
A copper wire is put into silver nitrate. Magnetite, an ore of iron, is smelted in large hot furnaces by blowing carbon monoxide gas through the ore. Lead metal and lead IV oxide in sulfuric acid produce lead II sulfate and water. Concentrated nitric acid is put on copper wire. Potassium dichromate and hydrochloric acid in solution will make chlorine gas, water, chromium III chloride and potassium chloride.