Choose the correct order of density of the alkali metals :

The geometry around boron in the product 'B' formed from the following reaction is

$$ \begin{aligned} &\mathrm{BF}_{3}+\mathrm{NaH} \stackrel{450 \mathrm{~K}}{\rightarrow} \mathrm{A}+\mathrm{NaF} \\\\ &\mathrm{A}+\mathrm{NMe}_{3} \rightarrow \mathrm{B} \end{aligned} $$

The interhalogen compound formed from the reaction of bromine with excess of fluorine is a :

The photochemical smog does not generally contain :