An ideal mono-atomic gas is heated at constant pressure. The...

Heat supplied at constant pressure is given by $\Delta Q = n C_p \Delta T$

Increase in internal energy is given by $\Delta U = n C_v \Delta T$

The fraction of total energy applied which increases the internal energy is $\dfrac{\Delta U}{\Delta Q} = \dfrac{n C_v \Delta T}{n C_p \Delta T} = \dfrac{C_v}{C_p}$

For an ideal mono-atomic gas, $C_v = \dfrac{3}{2} R$ and $C_p = \dfrac{5}{2} R$

Fraction = $\dfrac{\dfrac{3}{2} R}{\dfrac{5}{2} R} = \dfrac{3}{5}$

Answer: $\dfrac{3}{5}$