When hydrochloric acid is added to cobalt nitrate solution at room temperature, following reaction takes place and the reaction mixture becomes blue. On cooling the mixture it becomes pink

[Co(H2O)6]3+(Pink)(aq)+4Cl-(aq)⇌[CoCl4]2-(Blue)(aq)+6H2O(l)

On the basis of information given above, mark the correct answer

1. $∆\mathrm{H}>0$ for the reaction

2, $∆\mathrm{H}<0$ for the reaction

3. $∆\mathrm{H}=0$ for the reaction

4. The sign of $∆\mathrm{H}$ cannot be predicted on the basis of the given information.

Hint: For endothermic reaction, equilibrium shifts in forward direction on heating.
In this reaction,
$\underset{\left(\mathrm{Pink}\right)}{{\left[\mathrm{Co}\left({\mathrm{H}}_{2}{\mathrm{O}}_{6}\right)\right]}^{3+}}\left(\mathrm{aq}\right)+4{\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)⇌\underset{\left(\mathrm{Blue}\right)}{{\left[{\mathrm{CoCl}}_{4}\right]}^{2-}}\left(\mathrm{aq}\right)+6{\mathrm{H}}_{2}\mathrm{O}\left(\mathrm{l}\right)$
On cooling, the equilibriums shifts backward direction or on heating, the equilibrium shifts toward forward direction. Hence,
reaction is endothermic, i.e., $∆\mathrm{H}>0$.