Work done by an ideal gas at a constant volume is

Which statement is correct?

When a system goes from state $A$ to state $B$,the change in internal energy is $40 \, kJ/mol$. If the system returns from state $B$ to state $A$ via a reversible path and then returns to state $A$ via an irreversible path,what is the net change in internal energy?

The difference between $\Delta H$ and $\Delta U$ is usually significant for systems consisting of:

Which of the following are extensive properties?
$(A)$ Heat capacity
$(B)$ Entropy
$(C)$ Gibbs' energy
$(D)$ Concentration
$(E)$ Vapour pressure

Which of the following is an extensive property?