(i) Sugar crystals in cold water.

(ii) Sugar crystals in hot water.

(iii) Powdered sugar in cold water.

(iv) Powdered sugar in hot water.

Correct Answer: (iv) Powdered sugar in hot water

Explanation: Powdered sugar dissolves faster in hot water than in cold water because hot water is much stronger than cold water. When water is heated, the molecules gain energy and, as a result, move faster. As they move faster, they come in contact with sugar more often, causing them to melt faster.