Writing the units of all the terms of Right Hand Side, in $SI$ units

$n=\frac{(P a) \times\left(m^{3}\right)}{(J / mol / k) \cdot(k)}$

$n=\frac{\left(\frac{N}{m^{2}}\right) \cdot\left(m^{3}\right)}{\left(\frac{J}{\text { mol. K }}\right) \cdot(k .)}$

$n=\frac{\frac{ kgm }{ s ^{2} \cdot m ^{2}} \cdot m ^{3}}{\frac{ kg m ^{2}}{ s ^{2} \cdot mol \cdot K } \cdot K .}$

$n=\operatorname{mol}$. [All other terms cancel out]

Correct choice - option - $D$