A gas mixture contains $$25 \% \mathrm{~He}$$ and $$75 \% \mathrm{~CH}_4$$ by volume at a given temperature and pressure. The percentage by mass of methane in the mixture is approximately _________.

A metal exists as an oxide with formula $$M_{0.96}$$ O. Metal, $$M$$ can exist as $$M^{2+}$$ and $$M^{3+}$$ in its oxide $$M_{0.96} \mathrm{O}$$. The percentage of $$\mathrm{M}^{3+}$$ in the oxide is nearly

The mass of $$\mathrm{AgCl}$$ precipitated when a solution containing $$11.70 \mathrm{~g}$$ of $$\mathrm{NaCl}$$ is added to a solution containing $$3.4 \mathrm{~g}$$ of $$\mathrm{AgNO}_3$$ is [Atomic mass of $$\mathrm{Ag}=108$$, Atomic mass of $$\mathrm{Na}=23$$]