Calculate the number of atoms in the following: $(i)$ $52 \ mol$ of $Ar$ $(ii)$ $52 \ u$ of $He$ $(iii)$ $52 \ g$ of $He$

(N/A) $(i)$ $1 \ mol$ of $Ar = 6.022 \times 10^{23}$ atoms of $Ar$.
$52 \ mol$ of $Ar = 52 \times 6.022 \times 10^{23} = 3.131 \times 10^{25}$ atoms of $Ar$.
$(ii)$ Atomic mass of $He = 4 \ u$.
$4 \ u$ is the mass of $1$ atom of $He$.
Therefore,$52 \ u$ of $He$ contains $= \frac{52}{4} = 13$ atoms of $He$.
$(iii)$ Gram atomic mass of $He = 4 \ g$.
$4 \ g$ of $He$ contains $6.022 \times 10^{23}$ atoms.
Therefore,$52 \ g$ of $He$ contains $= \frac{6.022 \times 10^{23} \times 52}{4} = 7.8286 \times 10^{24}$ atoms.