Predict in which of the following entropy of system increases / decreases : 

(P) A liquid crystallizes into a solid

(Q) Temperature of a crystalline solid is raised

(R) $2{\mathrm{NaHCO}}_3\left(\mathrm{s}\right)⟶{\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$

(S) ${\mathrm{H}}_2\left(\mathrm{g}\right)⟶2\mathrm{H}\left(\mathrm{g}\right)$

(P) As particles are more densely packed in solids than in liquids, there is less disorder and less entropy, which results in a drop in entropy.
(Q) if the temperature of a crystalline solid is increased from 0 K to 115 K.
As the temperature rises, the solid will begin to melt, increasing entropy (the degree of disorder).
(R) Because there are two times as many molecules in the reactant as there are in the product, entropy is rising.
(S) Because there are now two species instead of just one, entropy has increased.