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

$K-40$ is a natural radioactive isotope which constitutes $0.012\%$ of natural potassium. If a cup of milk contains $370 \ mg$ of $K$,how many atoms of $K-40$ are ingested?

The number of moles of $BaCO_3$ which contain $1.5$ moles of oxygen atoms is:

$7.0 \, g$ of $N_2$,$8.0 \, g$ of $O_2$,and $34.0 \, g$ of $NH_3$ are present in a $1 \, L$ vessel. The active masses in $mol \, L^{-1}$ are respectively:

The mass of $0.1 \ mol$ of methane $(CH_4)$ is ...... $g$.

The number of atoms in $0.004 \ g$ of magnesium is: