Solubility curve of  $N{a}_{2}S{O}_4.10H_{2}O$ in water with temperature is given as

From the figure, we can say that

Below 34 ^∘ C , Na₂SO₄ .10 H₂O exists as such, since in this part solubility increases. This implies that process must be endothermic. Thereafter, solubility decrease with rise in temperature. It means that the solution process is exothermic. In fact after 34 ^∘ C, the substance exists in anhydrous state Na₂SO₄.