Define chemical change.

Define physical change.

Distinguish physical change and chemical change.

Melting of wax is a physical change but burning of wax is a chemical change. Explain, why?

Which of the following are chemical change? Growth of a plant, Rusting of iron, Mixing of iron fillings and sand, Cooking of food, Digestion of food, Freezing of water, burning of a candle.

Define void.

Define lens.

Define Valency