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

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 molarity of $$1 \mathrm{~L}$$ orthophosphoric acid $$\left(\mathrm{H}_3 \mathrm{PO}_4\right)$$ having $$70 \%$$ purity by weight (specific gravity $$1.54 \mathrm{~g} \mathrm{~cm}^{-3}$$) is __________ $$\mathrm{M}$$.

(Molar mass of $$\mathrm{H}_3 \mathrm{PO}_4=98 \mathrm{~g} \mathrm{~mol}^{-1}$$)

Number of moles of methane required to produce $$22 \mathrm{~g} \mathrm{~CO}_{2(\mathrm{~g})}$$ after combustion is $$\mathrm{x} \times 10^{-2}$$ moles. The value of $$\mathrm{x}$$ is _________.

Molar mass of the salt from $$\mathrm{NaBr}, \mathrm{NaNO}_3, \mathrm{KI}$$ and $$\mathrm{CaF}_2$$ which does not evolve coloured vapours on heating with concentrated $$\mathrm{H}_2 \mathrm{SO}_4$$ is ________ $$\mathrm{g} \mathrm{~mol}{ }^{-1}$$.

(Molar mass in $$\mathrm{g} \mathrm{~mol}^{-1}: \mathrm{Na}: 23, \mathrm{~N}: 14, \mathrm{~K}: 39, \mathrm{O}: 16, \mathrm{Br}: 80, \mathrm{I}: 127, \mathrm{~F}: 19, \mathrm{Ca}: 40)$$