Which one of the following processes involves chemical reactions?

$(a)$ Why is the corrosion of iron a serious problem?
$(b)$ How can we prevent corrosion?

Why is a combustion reaction considered an oxidation reaction?

Giving chemical equations,answer the following:
$(a)$ What happens when copper is heated in air?
$(b)$ What happens when the product obtained in the above reaction is heated in hydrogen?

Write a balanced chemical equation for each of the following reactions and also classify them.
$(a)$ Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.
$(b)$ $A$ piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas.

Explain the type of reactions represented by the following equations:
$(i)$ $CaO + CO_2 \longrightarrow CaCO_3$
$(ii)$ $2Na + 2H_2O \longrightarrow 2NaOH + H_2$