Answer:
Option A
Explanation:
(A) $CO_{2}(s) \rightarrow CO_{2}(g)$
It is just a phase transition (sublimation) as no chemical change has occurred. Sublimation is always endothermic. Product is gas, more disordered, hence $\triangle $ s is positive
(B) $CaCO_{3}(s) \rightarrow CaO(s)+CO_{2}(g)$
It is a chemical decomposition, not a phase change. Thermal decomposition occurs at the expense of energy, hence endothermic. Product contains a gaseous species, hence $\triangle S>0$
(C) $2H \rightarrow H_{2}(g)$
A new H-H covalent bond is formed, hence, $\triangle H <0.$ Also, the product is less disordered than the reactant, $\triangle S <0$
(D) Allohopes are considered as different phase, hence $P_{(white,solid)} \rightarrow P_{red,solid)}$ transition as well as allotropic change.
Also. red phosphorus is more ordered than white phosphorus, $\triangle$ S< 0.
