The atomic numbers of the elements $X, Y, Z$ are $a, a+1, a+2$ respectively. $Z$ is an alkali metal. The nature of bonding in the compound formed by $X$ and $Z$ is

The sets of molecules in which central atom has no lone pair of electrons are

I. $\mathrm{SnCl}_2, \mathrm{NH}_3, \mathrm{SF}_4$

II. $\mathrm{HgCl}_2, \mathrm{SO}_3, \mathrm{SF}_6$

III. $\mathrm{BeCl}_2 \mathrm{BF}_3, \mathrm{PCl}_5$

IV. $\mathrm{ClF}_3, \mathrm{BrF}_5, \mathrm{XeF}_6$

The number of lone pairs of electrons on the central atom of $\mathrm{XeO}_3, \mathrm{XeOF}_4$ and $\mathrm{XeF}_6$ respectively is

In which of the following options, the molecules are correctly arranged in the increasing order of their bond angles?