(a) Burning of candle - When a candle burns, the oxygen in the air reacts, formation of carbon dioxide takes place.
(b) Milk sours in hot and humid weather - Due to hot and humid weather lactose sugar present in the milk is converted into lactic acid which is a new substance formed
(c) Decomposition of water into hydrogen and Oxygen.- hydrogen and oxygen gases are produced from liquid water. The electrolysis of water causes a chemical change in which water molecules are split to form hydrogen and oxygen—two substances that are chemically different from water.
(d) Rusting of iron - When the iron is exposed to air and moisture, rust formation takes place. Rust is nothing but iron oxide; a new substance formed out of the reaction. The colour of the surface of the iron also changes. Hence, rusting of iron is a chemical change
(e) A frog breathes heavily - it is a chemical process as it utilizes this oxygen to break food to release energy