Maharashtra Board Solutions for Chapter: Composition of Matter, Exercise 6: Use your brain power

Deduce the molecular formulae of the compounds formed from the following pairs of elements.
H (valency 1) and O (valency 2).

Deduce the molecular formulae of the compounds formed from the following pairs of elements.  N (valency 3) and H (valency 1).

Deduce the molecular formulae of the compounds formed from the following pairs of elements. Fe (valency 3) and S (valency 2).

The valencies of the atom $\mathrm{H}, \mathrm{O}$ and $\mathrm{N}$ are $1, 2$ and $3$ respectively. The molecular formulae of these gaseous elements are ${\mathrm{H}}_2$, ${\mathrm{O}}_2$, and ${\mathrm{N}}_2$ respectively. How many chemical bonds are there in each of these molecules?