A student grows plants in different soils. What is the independent variable?

Correct answer: Type of soil

The direct answer is A: type of soil. The independent variable is the factor that the investigator deliberately changes to study its effect. Here, the student grows plants in different soils, so soil type is the planned difference. The plant’s growth may then be compared while other conditions, such as plant kind, water, light, and time, are kept as similar as possible. Option A is correct because it is changed by the student. Option B, plant height, is usually a dependent variable: it is measured as a possible result of the soil. Option C, number of leaves, is also a possible measured result, so it is another dependent variable, not the deliberately changed factor. Option D, time of measurement, is a condition or procedure detail; unless the investigation specifically changes time as the tested factor, it is not the independent variable in this question. The key chain is: change one factor, observe the response, and record the response. Memory cue: independent means “I change it”; dependent means “the result depends on it.”