One mole of diatomic ideal gas undergoes a cyclic process $ABC$ as shown in figure. The process $BC$ is adiabatic. The temperatures at $A, B\; and\; C$ are $400 K,800 K\; and\; 600 K$ respectively. Choose the correct statement.
$\begin{array}{1 1}(A)\;\text{The change in internal energy in the process AB is – 350R} \\ (B)\;\text{The change in internal energy in the process BC is –500R} \\(C)\;\text{The change in internal energy in whole cyclic process is 250 R} \\(D)\;\text{The change in internal energy in the process CA is 700 R}\end{array}$