The non-metal $\mathrm{A}$ is an important constituent of our food and most of the fuels around us. $\mathrm{A}$ forms two oxides $\mathrm{B}$ and $\mathrm{C}$. The oxide $\mathrm{B}$ is poisonous whereas oxide $\mathrm{C}$ causes global warming. 
(a) Identify $\mathrm{A}, \mathrm{B}$ and $\mathrm{C}$. 
(b) To which group of periodic table does $\mathrm{A}$ belong? 
(c) Name another element which is placed in the same group as $\mathrm{A}$.

A non-metal $\mathrm{X}$ which is the largest constituent of air combines with hydrogen when heated in the presence of iron as catalyst to form a gas $\mathrm{Y}$. When gas $\mathrm{Y}$ is treated with sulphuric acid, it forms a compound $\mathrm{Z}$ which is used as a chemical fertiliser.

Name the period of periodic table in which $\mathrm{X}$ is placed.

A non-metal $\mathrm{X}$ which is the largest constituent of air combines with hydrogen when heated in the presence of iron as catalyst to form a gas $\mathrm{Y}$. When gas $\mathrm{Y}$ is treated with sulphuric acid, it forms a compound $\mathrm{Z}$ which is used as a chemical fertiliser.

Which element is placed just before $\mathrm{X}$ in the period?

A non-metal $\mathrm{X}$ which is the largest constituent of air combines with hydrogen when heated in the presence of iron as catalyst to form a gas $\mathrm{Y}$. When gas $\mathrm{Y}$ is treated with sulphuric acid, it forms a compound $\mathrm{Z}$ which is used as a chemical fertiliser.

Which element is placed just after $\mathrm{X}$ in the period?