For an ideal gas, the internal energy depends upon its __________ only.

Answer: Option B

Actually the internal energy ($$U$$) of a substance is a function of $$dU=CvdT-\left[P+T\left(\frac{\left(\frac{\partial V}{\partial T}\right)P}{\left(\frac{\partial V}{\partial P}\right)T}\right)dV\right]$$

For an ideal gas, $$PV=RT$$

So, $$\left(\frac{\partial V}{\partial T}\right)P=\frac{R}{P}$$   and  $$\left(\frac{\partial V}{\partial P}\right)T=-\frac{RT}{P^2}$$
Hence, $$dU=CvdT$$
So, Internal energy of an ideal gas is purely a function of temperature. (Here the $$C_V$$ is considered only as a function of temperature which is satisfied by many of the substances.)