Calculate the number of molecules present in $5.4 \ g$ of urea (Molar mass of urea $= 60 \ g \ mol^{-1}$).

Which has the highest number of atoms?

Which of the following contains the maximum number of atoms?

$2.8 \times 10^{-3} \ mol$ of $CO_2$ is left after removing $10^{21}$ molecules from its '$x$' $mg$ sample. The mass of $CO_2$ taken initially is. Given: $N_A = 6.02 \times 10^{23} \ mol^{-1}$. (in $mg$)

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

$1 \text{ g}$ of $H_2$ contains the same number of molecules as in