Which one of the following is always not negative?

The heat of combustion $\left(kJ \ mol^{-1}\right)$ is highest for

For the reaction $2Cl_{(s)} \to Cl_{2(s)}$,the signs of $\Delta H$ and $\Delta S$ respectively are

Consider the following data for the reaction $X_2(g) + Y_2(g) \rightleftharpoons 2XY(g)$ at $600 \ K$. The $\Delta_r G^\circ$ (in $kJ \ mol^{-1}$) for the reaction is:

Compound	$\Delta_f H^\circ$ $(kJ \ mol^{-1})$	$S^\circ$ $(J \ mol^{-1} \ K^{-1})$
$XY(g)$	$42$	$200$
$X_2(g)$	$8$	$140$
$Y_2(g)$	$80$	$250$

What is the difference between $\Delta H$ and $\Delta U$ for the combustion of methane at $25\,^oC$?

For the gas phase reaction,$PCl_{5(g)} \rightleftharpoons PCl_{3(g)} + Cl_{2(g)}$,which of the following conditions are correct?