When hydrochloric aicd is addded to cobalt and nitrate solution at room temperautre, the following reaction takes place and the reaction mixture becomes blue. On cooling the mixture it becomes pink. On the basis of this information mark the corect ansewer.
`underset("pink")[[Co(H_(2)O)_(6)]]^(3+)(aq)+4CI^(-)hArr`
`underset("blue")[CoCI_(4)]^(2-)(aq)+6H_(2)O(l)`

Options

A. `DeltaH gt 0` for the reaction
B. `DeltaH lt 0` for the reaction
C. `DeltaH =0` for the reaction
D. The sign of `DeltaH` cannot be predicted on the basis of this information.

Answer

A

Explanation

Since the reaction shifts to backward direction on cooling, this means that the backward reaction is exothermic reaction. Therefore, the forward reaction is endothermic reaction and `DeltaH > 0`.