The number of moles of $Mg_3(PO_4)_2$ containing $0.25$ moles of oxygen atoms is:

What is the number of moles present in $1 \ m^3$ of any gas at $STP$?

Calculate the number of molecules in $18 \ mg$ of water in terms of Avogadro's number $(N_A)$.

Find the number of hydrogen atoms present in $6.0 \ g$ of urea $(NH_2CONH_2)$:

Arrange the following in order of increasing mass:
$I$. $1$ mole of $N_2$
$II$. $0.5$ mole of $O_3$
$III$. $3.011 \times 10^{23}$ molecules of $O_2$
$IV$. $0.5$ gram atom of $O$

Which of the following contains $6.02 \times 10^{22}$ molecules?