If $24 \times 10^{23}$ molecules are removed from $50 \ g$ of hydrogen gas $(H_2)$,how many moles of hydrogen remain?

Natural abundances of $^{12}C$ and $^{13}C$ isotopes of carbon are $99\,\%$ and $1\,\%$,respectively. Assuming they only contribute to the molecular weight of $C_2F_4$,the percentage of $C_2F_4$ having a molecular mass of $101$ is $.....$

The number of molecules and the number of atoms present in $1 \ g$ of nitrogen are respectively .....

The number of water molecules in $250\, mL$ of water is closest to $.....\, \times 10^{23}$.
[Given: density of water is $1.0\, g\, mL^{-1}$; Avogadro's number $= 6.023 \times 10^{23}$]

The number of moles of water present in a spherical water droplet of radius $1.0 \ cm$ is,(Given: Density of water in the droplet $= 1.0 \ g \ cm^{-3}$)

The mass of $4.48 \ dm^3$ of a certain gas is $5.6 \ g$ at $STP$. Assuming ideal behaviour,identify the probable gas from the following.