c
In cyclic process, change in total internal energy is zero.
$\Delta {U_{cyclic}} = 0$
$\Delta {U_{BC}} = n{C_v}\Delta T = 1 \times \frac{{5R}}{2}\Delta T$
$Where,{C_v} = molar\,specific\,heat\,at\,constant\,volume.$
$For\,BC,\Delta T = - 200K$
$\therefore \,\,\Delta {U_{BC}} = - 500R$