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

$2 \, g$ 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.

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

Why do we store silver chloride in dark-coloured bottles?

Write the chemical equation of the reaction with an example in which a change in temperature takes place.

On heating blue coloured powder of copper $(II)$ nitrate in a boiling tube,copper oxide (black),oxygen gas and a brown gas $X$ is formed.
$(a)$ Write a balanced chemical equation of the reaction.
$(b)$ Identify the brown gas $X$ evolved.