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

Write true or false for the following statement:
The insoluble substance formed during a chemical reaction is known as a precipitate.

$(a)$ Define corrosion.
$(b)$ What is corrosion of iron called?
$(c)$ How will you recognise the corrosion of silver?

$A, B$ and $C$ are three elements which undergo chemical reactions according to the following equations:
$A_{2}O_{3} + 2B \rightarrow B_{2}O_{3} + 2A$
$3CSO_{4} + 2B \rightarrow B_{2}(SO_{4})_{3} + 3C$
$3CO + 2A \rightarrow A_{2}O_{3} + 3C$
Answer the following questions with reasons:
$(a)$ Which element is the most reactive?
$(b)$ Which element is the least reactive?
$(c)$ What is the type of reactions listed above?

What happens when a piece of $(i)$ Silver metal is added to copper sulphate solution? Also,write the balanced chemical equation if the reaction occurs.

Write two observations for the following chemical reaction:
$(a)$ Potassium iodide solution is added to lead nitrate solution.