Answer :
1. (a) Frost forming as the temperature drops on a humid winter night is primarily a physical change. This is because the change from water vapor to ice crystals is a change in state (from gas to solid) without altering the chemical composition of the substance.
2. (b) The growth of a cornstalk from a seed that is watered and fertilized is primarily a chemical change. This is because the process involves complex biochemical reactions within the seed leading to growth, involving the conversion of nutrients and water into plant tissues.
3. (c) The ignition of a match to form ash and a mixture of gases is primarily a chemical change. This is due to the combustion reaction that occurs when the match is ignited, leading to the formation of new substances (ash and gases) with different chemical properties than the original match.
4. (d) The evaporation of perspiration when you relax after jogging is primarily a physical change. This is because the change involves the phase transition of liquid sweat to water vapor without altering the chemical composition of the sweat.
5. (e) The tarnishing of a silver fork slowly in air is primarily a chemical change. This is because the silver reacts with substances in the air (such as sulfur compounds) to form a new compound on the surface of the fork, altering its chemical composition and appearance over time.
