Question

state one instance where water undergo physical change and another which undergo chemical change . substantiate your answer?

Answer 1

Physical change of water:
Melting of solid water(ice) to liquid water is a physical change as constituent molecules are same before and after the change and no new product is formed.
Chemical change:
Reaction of water with Na₂O to form NaOH is chemical change as water molecule lost its identity after the chemical reaction and new molecule NaOH have different properties than water.
Na₂O + H₂O------->2 NaOH