Consider the following reaction :

$$ 3 \mathrm{PbCl}_2+2\left(\mathrm{NH}_4\right)_3 \mathrm{PO}_4 \rightarrow \mathrm{Pb}_3\left(\mathrm{PO}_4\right)_2+6 \mathrm{NH}_4 \mathrm{Cl} $$

If $72 ~\mathrm{mmol}$ of $\mathrm{PbCl}_2$ is mixed with $50 ~\mathrm{mmol}$ of $\left(\mathrm{NH}_4\right)_3 \mathrm{PO}_4$, then the amount of $\mathrm{Pb}_3\left(\mathrm{PO}_4\right)_2$ formed is ________ mmol (nearest integer).

The number of molecules/ion/s having trigonal bipyramidal shape is _______.

$\mathrm{PF}_5, \mathrm{BrF}_5, \mathrm{PCl}_5,\left[\mathrm{Pt} \mathrm{Cl}_4\right]^{2-}, \mathrm{BF}_3, \mathrm{Fe}(\mathrm{CO})_5$

The lowest oxidation number of an atom in a compound $\mathrm{A}_2 \mathrm{B}$ is -2 . The number of electrons in its valence shell is _______.

$\mathrm{K}_{\mathrm{a}}$ for $\mathrm{CH}_3 \mathrm{COOH}$ is $1.8 \times 10^{-5}$ and $\mathrm{K}_{\mathrm{b}}$ for $\mathrm{NH}_4 \mathrm{OH}$ is $1.8 \times 10^{-5}$. The $\mathrm{pH}$ of ammonium acetate solution will be _________.