How many moles of electrons will weigh $1 \ kg$?

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 $.....$

Which gas among the following contains the maximum number of molecules at $STP$? (Molar masses in $g \ mol^{-1}$: $CO_{2}=44, Ar=39.9, CH_{4}=16, O_{2}=32$)

The number of atoms in $558.5 \ g$ of $Fe$ is equal to: [Atomic mass of $Fe = 55.85 \ g/mol$]

The largest number of molecules is in

Number of atoms present in $224 \, dm^3$ of oxygen gas at $STP$ is