Which of the following statements is true about internal energy?

The formation of water from $H_{2(g)}$ and $O_{2(g)}$ is an exothermic reaction because

Which of the following compounds is $NOT$ present in its standard state at $25^{\circ} C$ and $1 \text{ atmosphere}$ pressure?

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

Although heat is a path function,heat absorbed by the system under certain specific conditions is independent of path. What are those conditions? Explain.

Consider the expansion given in problem $6.2$,for $1 \, mol$ of an ideal gas conducted reversibly.