Chemical Bonding and Molecular Structure

Structure of $\mathrm{XeO}_4$ and $\mathrm{XeO}_3 \mathrm{F}_2$ do not have any lone pair at central-atom. i.e.

Thus, option (a) is the correct. While in $\mathrm{XeO}_3, \mathrm{XeO}_2 \mathrm{~F}_2$ and $\mathrm{XeF}_6$ one lone pair of electrons is present on central atom of each compound.

More the covalent nature of compounds lesser will be its solubility.

Also, according to Fajan's rule, lesser be the size of cation or more be size of anion, species show more covalent nature.

As, $\mathrm{Mg}$ show +2 oxidation state and $\mathrm{Na}$ is in +1 oxidation state the size of $\mathrm{Mg}^{2+}$ is less than that of $\mathrm{Na}^{+}$. On the other hand, sulphur is in $-2$ oxidation state while chlorine is in $-1$ oxidation state, therefore sulphur anion is larger in size. Thus, among the given species, the combination of $\mathrm{Mg}$ and sulphur ($\mathrm{S}$) show maximum covalent nature and therefore is least soluble.

Hence, option (b) is the correct.

Isostructural species have same structure and same number of lone pair of electrons over central atom.

The structure of BO$^{-3}_3$ is

Thus, these are not isostructural because sulphur has one lone pair in its structure. Thus, both assertion and reason are correct and given reason is the correct answer of the given assertion. Hence, option (a) is the correct.

Due to hydration, addition of $\mathrm{H}_2 \mathrm{O}$ is by Markownikoff's rule and by hydroboration oxidation, addition of $\mathrm{H}_2 \mathrm{O}$ is by anti-Markownikoff's rule.

The structure of $\mathrm{IF}_7$ is pentagonal bipyramidal.

It can be depicted as follow

($Z=53$) (Ground state) $=$

I (Excited state) =

Here, $X$ denotes electrons of $\mathrm{F}$-atoms. The structure of $\mathrm{IF}_7$ is shown below :

The bond enthalpies of the two $\mathrm{O}-\mathrm{H}$ bonds in $\mathrm{H}-\mathrm{O}-\mathrm{H}$ are not equal. This is because electronic environment around $\mathrm{O}$ is not same after breakage of one $\mathrm{O}-\mathrm{H}$ bond. Therefore, both assertion and reason are incorrect.