The following are chemical changes:
(b) Rusting of iron – This is a chemical change because iron reacts with oxygen in the air to form iron oxide (rust), a new substance with different properties.
(d) Cooking of food – This involves chemical reactions that change the molecular structure of the food, resulting in new substances.
(e) Digestion of food – In digestion, food is broken down by enzymes into simpler substances, which is a chemical process.
(g) Burning of a candle – When a candle burns, the wax (a hydrocarbon) reacts with oxygen in the air, producing carbon dioxide, water, and heat. This is a chemical change.
(a) Growth of a plant – This involves a series of biochemical processes, but it's not considered a simple chemical change, as it involves the synthesis of new compounds through photosynthesis.
(c) Mixing of iron filings and sand – This is a physical change because no new substances are formed, and the iron filings and sand can be easily separated.
(f) Freezing of water – This is a physical change because water changes from liquid to solid, but its chemical composition remains the same.