For which one of the following reactions,the entropy change is positive?

Question

(a) $H_2+\large\frac{1}{2} $$O_2 \to H_2 O$

(b) $Na^{+}+Cl^{-} \to NaCl$

(c) $NaCl \to NaCl$

(d) $H_2O \to H_2O$