Answer
Ar(g).
Work Step by Step
Entropies of gases are usually much larger than those of solids. So, Ar(g) is expected to have greater entropy than that of Ca(s).
We see from table 16.1 that our prediction is correct.
$S^{\circ}(Ca,s)=41.42\,JK^{-1}mol^{-1}$
$S^{\circ}(Ar,g)=154.7\,JK^{-1}mol^{-1}$
