Question

electrolysis of water or Na2Cl exposed in sunlight is a chemical change?

Answer 1

All electrolysis involve oxidation and reduction. The principal representative of such changes are electrons. Electrolysis of water involves reduction of hydrogen ion to dihydrogen and oxidation of hydroxyl ion to dioxygen. Hence it's a chemical change.

Exposure of NaCl solution to sunlight as happen during making of NaCl from sea water in the open is mere a process of precipitation governed by the principle of solubility and ionic product of [Na+] & [Cl-]. Hence it cannot be classified as a chemical change.