The total number of molecules with zero dipole moment among $$\mathrm{CH}_4, \mathrm{BF}_3, \mathrm{H}_2 \mathrm{O}, \mathrm{HF}, \mathrm{NH}_3, \mathrm{CO}_2$$ and $$\mathrm{SO}_2$$ is ________.

Standard enthalpy of vapourisation for $$\mathrm{CCl}_4$$ is $$30.5 \mathrm{~kJ} \mathrm{~mol}^{-1}$$. Heat required for vapourisation of $$284 \mathrm{~g}$$ of $$\mathrm{CCl}_4$$ at constant temperature is ________ $$\mathrm{kJ}$$.

(Given molar mass in $$\mathrm{g} \mathrm{mol}^{-1} ; \mathrm{C}=12, \mathrm{Cl}=35.5$$)

If $$50 \mathrm{~mL}$$ of $$0.5 \mathrm{M}$$ oxalic acid is required to neutralise $$25 \mathrm{~mL}$$ of $$\mathrm{NaOH}$$ solution, the amount of $$\mathrm{NaOH}$$ in $$50 \mathrm{~mL}$$ of given $$\mathrm{NaOH}$$ solution is ______ g.

The following concentrations were observed at $$500 \mathrm{~K}$$ for the formation of $$\mathrm{NH}_3$$ from $$\mathrm{N}_2$$ and $$\mathrm{H}_2$$. At equilibrium ; $$\left[\mathrm{N}_2\right]=2 \times 10^{-2} \mathrm{M},\left[\mathrm{H}_2\right]=3 \times 10^{-2} \mathrm{M}$$ and $$\left[\mathrm{NH}_3\right]=1.5 \times 10^{-2} \mathrm{M}$$. Equilibrium constant for the reaction is ________.