Among the following given substances, the one with zero $\Delta_f H^{\circ}$ is

If 92 g Na reacts with water in open vessel at 300 K . What is the value of work done?

[Assume ideal nature of the gaseous product.]

For the reactions,

$$ \begin{aligned} 2 \mathrm{Cl}(g) & \longrightarrow \mathrm{Cl}_2(g) \\ \mathrm{CO}_2(g) & \longrightarrow \mathrm{CO}(g)+\frac{1}{2} \mathrm{O}_2(g) \end{aligned} $$

What are the signs of $\Delta S$, respectively?

Which of the following statement is correct?