When solid $\mathrm{NaF}$ is treated with cone. ${\mathrm{H}}_2{\mathrm{SO}}_4$ in a test tube, followed by warming, then dimeric form of a gas is evolved, by which the test tube acquires a greasy appearance on its walls. Subsequently, the gas liberated when brought in contact with moistened glass rod forms a deposit which contains :

When solid $\mathrm{NaF}$ is treated with cone. ${\mathrm{H}}_2{\mathrm{SO}}_4$ in a test tube, followed by warming, then dimeric form of a gas is evolved, by which the test tube acquires a greasy appearance on its walls. Subsequently, the gas liberated when brought in contact with moistened glass rod forms a deposit which contains 

${\mathrm{H}}_2{\mathrm{SiF}}_6$, ${\mathrm{SiO}}_2\cdot {\mathrm{H}}_2\mathrm{O}$ and ${\mathrm{H}}_2{\mathrm{SiO}}_3$.

Hence, options B, C and D are correct.