Problem 19 from NEET's Solved Paper 2013:
The amount of heat energy required to raise the temperature of $\pu{1 g}$ of helium at NTP from $T_1$ to $T_2$ (in kelvin) is
\begin{align} &\text{(a)}~\displaystyle\frac 3 8 N_\mathrm{A}k_\mathrm{B}(T_2 - T_1) &\quad &\text{(b)}~\displaystyle\frac 3 2 N_\mathrm{A}k_\mathrm{B}(T_2 - T_1) \\ &\text{(c)}~\displaystyle\frac 3 4 N_\mathrm{A}k_\mathrm{B}(T_2 - T_1) &\quad &\text{(d)}~\displaystyle\frac 3 4 N_\mathrm{A}k_\mathrm{B}\frac{T_2}{T_1} \end{align}
My chemistry teacher said the “language of question” gives away the process is isochoric and suggested to use the following equation to solve the problem:
$$\mathrm dQ = nC_V\Delta T = \frac f 2nR\Delta T$$
yielding the correct answer $\text{(a)}~\displaystyle\frac 3 8 N_\mathrm{A}k_\mathrm{B}(T_2 - T_1).$
How can this be deduced conceptually? What exactly points to an isochoric process in this case?