The number of moles in $620 \ g$ of sodium oxide is ..... moles.

Choose the correct option for the mole fraction of both components in a gaseous mixture containing $7 \ g$ of nitrogen and $8 \ g$ of oxygen.

How many moles of $Mg_{3}(PO_{4})_{2}$ contain $0.25$ moles of $O$ atoms?

Find the number of electrons present in $34 \ g$ of $NH_{3(g)}$. (Express your answer in terms of $N_A$)

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 $.....$

How many water molecules are there in one drop of water $($Volume $= 0.0018 \ mL)$ at room temperature?