Match the transformation in Column I with appropriate options in...

(A) $\mathrm{CO}_2(\mathrm{~s}) \longrightarrow \mathrm{CO}_2(\mathrm{~g})$ It is just a phase transition (sublimation) as no chemical change has occurred. Sublimation is always endothermic. Product is gas, more disordered, hence $\Delta s$ is positive. (B) $\mathrm{CaCO}_3(\mathrm{~s}) \longrightarrow \mathrm{CaO}(\mathrm{s})+\mathrm{CO}_2(\mathrm{~g})$ It is a chemical decomposition, not a phase change. Thermal decomposition occur at the expense of energy, hence endothermic. Product contain a gaseous species, hence, $\Delta S>0$. (C) $2 \mathrm{H} \longrightarrow \mathrm{H}_2(\mathrm{~g})$ A new $\mathrm{H}-\mathrm{H}$ covalent bond is being formed, hence, $\Delta H < 0$. Also, product is less disordered than reactant, $\Delta S < 0$. (D) Allotropes are considered as different phase, hence $\mathrm{P}_{\text{(white, solid) }} \rightarrow \mathrm{P}_{\text{(red, solid) }}$ is a phase transition as well as allotropic change. Also, red phosphorus is more ordered than white phosphorus, $\Delta S < 0$.