One mole of an ideal gas is kept in a rigid container of negligible...

For an isochoric process, the work done is zero. According to the first law of thermodynamics, the heat supplied is equal to the change in internal energy.

$\Delta Q = \Delta U = n C_v \Delta T$

Substituting the given values:

$3.0 = 1 \times C_v \times 1$

$C_v = 3.0 \text{ cal mol}^{-1} \text{ K}^{-1}$

The molar heat capacity at constant volume is related to the degrees of freedom $f$ by $C_v = \dfrac{f}{2} R$.

Using $R \approx 2 \text{ cal mol}^{-1} \text{ K}^{-1}$:

$3.0 = \dfrac{f}{2} \times 2$

$f = 3$

A gas with $3$ degrees of freedom is a monatomic gas. Among the given options, helium and argon are monatomic gases.