A student places surfaces of different colours in sunlight and measures temperature. What type of variable is surface colour?

Correct answer: Independent variable

The direct answer is A, surface colour as the independent variable. The independent variable is the feature deliberately changed between trials. Here surfaces of different colours are placed in sunlight, and temperature is measured. Therefore colour is the possible cause, while temperature is the dependent result. Step by step: prepare surfaces that differ in colour; keep material, size, thickness, position, sunlight exposure time and starting temperature as similar as possible; expose them; measure temperature; compare readings; hence colour is independent. A is correct. B is wrong because temperature is the measured dependent variable. C is wrong because a controlled variable is kept the same, whereas colour is intentionally different. D is wrong because a constant also remains unchanged, and the colours are not unchanged. The wording “different colours” is an important clue: it identifies the factor varied by the experimenter. A good experiment also needs repeated measurements and suitable control of other conditions. Memory cue: ask “what did the investigator change?”; that answer is independent.