How many moles of $Mg_3(PO_4)_2$ will contain $0.50 \ mol$ of oxygen atoms?

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 $H$ atoms in $27 \ g$ of water is .........

The molar mass of $CO_2$ is $44 \ g/mol$. Given that the Avogadro constant is $6.022 \times 10^{23} \ mol^{-1}$,the mass of one molecule of $CO_2$ is ..... $\times 10^{-23} \ g$.

Identify the number of moles of $H$ atoms present in $n$ moles of the organic compound represented as: (in $n$)

The total number of valence electrons in $4.2 \ g$ of $N_3^-$ ion is ............. $N_A$ ($N_A$ is the Avogadro's number).