What is the volume occupied by $16 \ g$ methane gas at $STP$ (in $cm^3$)?

The number of electrons in $2.1 \ g$-ion of $Cl^{-}$ is

One molecule of water has a volume of ........ $\times 10^{-23} \text{ cm}^3$? (Density of water = $1 \text{ g cm}^{-3}$)

What is the symbol for the $SI$ unit of mole? How is the mole defined?

$5.6 \, L$ of oxygen at $STP$ contains .............

Two vessels $A$ and $B$ of $1 \, L$ each contain $0.11 \, g$ $CO_2$ gas and $0.07 \, g$ of unknown gas respectively under the same conditions of pressure and temperature. The unknown gas is: