The correct answer is (a) a physical change that can be reversed.
Explanation:
When sugar dissolves in hot water, it’s a physical change because the sugar molecules are simply dispersed in the water, not forming a new substance. Cooling the solution then causes the sugar to crystallize out, which is again a physical change as the sugar is simply changing its state from liquid to solid. Since the original sugar can be redissolved in water, this is a reversible physical change.
Why other options are incorrect:
(b) chemical change that can be reversed:
A chemical change involves a change in the chemical composition of the substances involved. Dissolving sugar in water is a physical change, not a chemical change. While some chemical reactions can be reversed, the process of dissolving sugar in water is not one of them.
(c) physical change that cannot be reversed:
This is incorrect because the process of crystallization is the reverse of dissolving sugar, meaning the sugar can be recovered by re-dissolving it in water.
(d) chemical change that cannot be reversed:
This is incorrect for the same reasons as option (b). The change is physical, not chemical, and is reversible.