The colour formed on the surface of copper powder when it is heated in a china dish is:

The smell and taste of food containing fats and oils change after some time. Why does this happen? Name the process. List two ways which help to slow down the above-mentioned process.

Identify the type of reactions in each of the following reactions:
$(i)$ $Zn + H_{2}SO_{4} \longrightarrow ZnSO_{4} + H_{2}$
$(ii)$ $CaO + H_{2}O \longrightarrow Ca(OH)_{2}$

$A$ metal $X$ acquires a green colour coating on its surface on exposure to air.
$(i)$ Identify the metal $X$ and name the process responsible for this change.
$(ii)$ Name and write the chemical formula of the green coating formed on the metal.
$(iii)$ List two important methods to prevent this process.

An aluminium can was used to store ferrous sulphate solution. It is observed that in a few days,holes appeared in the can. Explain the observation and write the chemical equation to support your answer.

Give reasons for the following:
$(i)$ Keeping food in airtight containers helps in preventing rancidity.