One mole of an ideal monoatomic gas is heated at a constant pressure of one atmosphere from $0^{\circ }$C to ${100}^{\circ }$ C. Then the change in the internal energy is

The correct option is C

Change in internal energy is always equals to the heat supplied at constant volume.
i.e $△U=(△Q{)}_V=\mu C_V△T.$
For monoatomic gas $C_V=\frac{3}{2}R$
$\Rightarrow △U=\mu \left(\frac{3}{2}R\right)△T=1\times \frac{3}{2}\times 8.31\times (100-0)$
$=12.48\times {10}^{2}J$