Two rigid boxes containing different ideal gases are placed on a table. Box A contains one mole of nitrogen at temperature $T_0$, while Box $B$ contains one mole of helium at temperature $(7 / 3) T_0$. The boxes are then put into thermal contact with each other and heat flows between them until the gases reach a common final temperature. (Ignore the heat capacity of boxes). Then, the final temperature of the gases, $T_f$, in terms of $T_0$ is

• A

  $\mathrm{T}_{\mathrm{f}}=\frac{5}{2} \mathrm{~T}_0$
• B

  $\mathrm{T}_{\mathrm{f}}=\frac{3}{7} \mathrm{~T}_0$
• C

  $\mathrm{T}_{\mathrm{f}}=\frac{7}{3} \mathrm{~T}_0$
• Correct answer
  D

  $T_f=\frac{3}{2} T_0$

Hence, the correct answer is option: 'D'.