Name the type of reaction for the following:
$(i)$ Vegetable matter changing into compost.
$(ii)$ Burning of natural gas.

$(i)$ When a metal $X$ is added to the salt solution of a metal $Y$,the following chemical reaction takes place: Metal $X +$ Salt solution of $Y \rightarrow$ Salt solution of $X +$ Metal $Y$.
$(ii)$ Mention the inference you draw regarding the reactivity of metal $X$ and $Y$ and also about the type of reaction. State the reason for your conclusions.

Explain the type of reactions represented by the following equations:
$(i)$ $Mg + CuSO_4 \longrightarrow MgSO_4 + Cu$
$(ii)$ $NH_4NO_2 \longrightarrow N_2 + 2H_2O$

Name the type of reaction for the following:
$(i)$ Silver items turning black when left exposed to air.
$(ii)$ Change in colour of copper sulphate from blue to green on dipping an iron nail in it.

Give the characteristic tests for the following gases:
$(a)$ $O_2$
$(b)$ $H_2$

Observe the given figure and answer the following questions:
$(i)$ Write the complete balanced chemical equation for the reaction.
$(ii)$ Write the type of reaction involved.
$(iii)$ Is there any precipitate formed?
$(iv)$ If any precipitate is formed,write the colour of the precipitate.