In a controlled experiment, which variable is deliberately kept constant to isolate the effect of the independent variable?

• A. The control variable (constants)
• B. Random variable
• C. Dependent variable
• D. Independent variable

Answer: (A)

To isolate the effect of the factor you change, you keep all other conditions identical across all experiments. Those constant items are called control variables. By holding them steady, you remove alternative explanations for any change you observe in the outcome, so you can attribute differences specifically to the independent variable you’re testing. For example, if you’re testing how light intensity affects plant growth, you’d keep water, soil type, temperature, and pot size the same while varying only the light level. Any difference in growth is more reliably due to light, not other factors.

The thing you deliberately change is the independent variable, and the thing you measure is the dependent variable. Random variables represent unpredictable variation that you don’t deliberately set, and you don’t keep those constant because they’re inherent noise in the system.