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 $\underline{\hspace{2cm}}$$\mathrm{g} \mathrm{~mol}{ }^{-1}$. (Molar mass in $$\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)$$