A changeable factor in an experiment

• A. Variable
• B. Constant
• C. Control
• D. Parameter

Answer: (A)

The factor that you change to see its effect in an experiment is called a variable. By deliberately varying this factor across trials, you can observe how the outcome responds. A constant is something you keep the same so the test is fair. A control is a baseline condition used for comparison where the variable isn’t applied (or stays at a standard level). A parameter is typically a fixed value that defines or characterizes a system or model, not the factor you actively test by changing it.

For example, if you’re studying how light exposure affects seed germination, light exposure is the variable you change; soil type would be kept the same as a constant; a setup with no light serves as a control; and a parameter might be a growth-rate constant in a model used to predict germination under various conditions.