Following is the P vs V plot of a cyclic process $$1 \rightarrow 2$$, $$2 \rightarrow 3$$, $$3 \rightarrow 4$$, $$4 \rightarrow 1$$, denoted as I, II, III and IV respectively for a system of one mole of an ideal gas. Assume that there is heat exchange between the system and surroundings only in II and IV. Which of the following is/are correct?

A

In II and IV $$\Delta S$$ is zero

B

In I and III, $$\Delta S$$ is zero

C

I and III are isothermal and reversible

D

In II and IV, change in internal energy of the gas $$(\Delta U)$$ is zero