Which one of the following processes involves chemical reactions?

Which among the following is(are) double displacement reaction$(s)$?
$(i)$ $Pb + CuCl_{2} \rightarrow PbCl_{2} + Cu$
$(ii)$ $Na_{2}SO_{4} + BaCl_{2} \rightarrow BaSO_{4} + 2NaCl$
$(iii)$ $C + O_{2} \rightarrow CO_{2}$
$(iv)$ $CH_{4} + 2O_{2} \rightarrow CO_{2} + 2H_{2}O$

$A$ solution of potassium chloride when mixed with silver nitrate solution,an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of the chemical reaction?

On adding a drop of barium chloride solution to an aqueous solution of sodium sulphite,a white precipitate is obtained.
$(a)$ Write a balanced chemical equation of the reaction involved.
$(b)$ What other name can be given to this precipitation reaction?
$(c)$ On adding dilute hydrochloric acid to the reaction mixture,the white precipitate disappears. Why?

Which two observations will be made when quicklime is added to water? Mention two uses of the product obtained.

Give differences between the displacement and double displacement reactions.