Which of the following gases can be used for the storage of a fresh sample of an oil for a long time?

What happens when a piece of $Zn$ metal is added to $CuSO_4$ solution?

Complete the missing components/variables given as $x$ and $y$ in the following reactions:
$(a)$ $Zn(s) + H_2SO_4(aq) \longrightarrow ZnSO_4(x) + H_2(y)$
$(b)$ $CaCO_3(s) \xrightarrow{x} CaO(s) + CO_2(g)$

What happens when a piece of aluminium metal is added to dilute hydrochloric acid?

$2 \, g$ of ferrous sulphate crystals are heated in a boiling tube.
$(i)$ State the colour of ferrous sulphate crystals both before heating and after heating.
$(ii)$ Name the gases produced during heating.
$(iii)$ Write the chemical equation for the reaction.

During the reaction of some metals with dilute hydrochloric acid,following observations were made.
$(a)$ Silver metal does not show any change.
$(b)$ The temperature of the reaction mixture rises when aluminium $(Al)$ is added.
$(c)$ The reaction of sodium metal is found to be highly explosive.
$(d)$ Some bubbles of a gas are seen when lead $(Pb)$ is reacted with the acid.
Explain these observations giving suitable reasons.