Some elements and their valencies are given.

Elements	Valency
$$\begin{gathered} \mathrm{Zn} \\ \mathrm{O} \end{gathered}$$	$$\begin{gathered} 2 \\ 2 \end{gathered}$$

Write the chemical formula of zinc oxide.

$\mathrm{P}, \mathrm{Q}, \mathrm{R}, \mathrm{S}$ are four elements. Their atomic numbers are $8, 17, 12$ and $16$ respectively. Find the type of chemical bond in these compounds formed by combining the following pairs of elements.

(Electronegativity values: $\mathrm{P}=3.44, \mathrm{Q}=3.16, \mathrm{R}=1.31, \mathrm{S}=2.58$)

1. $\mathrm{P}, \mathrm{R}$
2. $\mathrm{P}, \mathrm{S}$
3. $\mathrm{Q}, \mathrm{R}$