On dissolving sugar in water at room temperature solution feels cool to touch. Under which of the following cases dissolution of sugar will be most rapid?
(i) Sugar crystals in cold water.
(ii) Sugar crystals in hot water.
(iii) Powdered sugar in cold water.
(iv) Powdered sugar in hot water.
The answer is the option (iv).
Dissolution is an endothermic process, which is why the solution is cool to touch. Also, powdered sugars have a higher surface area than sugar crystals which further promotes dissolution.