Complete the following reaction:
$2 FeSO_{4} \xrightarrow{\text{Heat}} Fe_{2}O_{3} + \dots + \dots$

Write two observations for the following chemical reaction:
$(a)$ Lead nitrate is strongly heated in a hard glass test tube.

When a green iron salt is heated strongly, its colour finally changes to black and the odour of burning sulphur is given out.
$(a)$ Name the iron salt.
$(b)$ Name the type of reaction that takes place during the heating of iron salt.

$A$ solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. $(i)$ State two types of this reaction.

Explain the type of reaction represented by the following equation:
$(i) \ CuSO_{4} + 2NaOH \longrightarrow Cu(OH)_{2} + Na_{2}SO_{4}$

In the electrolysis of water,why is the volume of gas collected over one electrode double that of the gas collected over the other electrode?