In an experiment, which variable is purposely changed by the experimenter?

• A. Dependent variable
• B. Controlled variable
• C. Independent variable
• D. Constant

Answer: (C)

In experiments, the factor you deliberately change to see its effect is the independent variable. This is the variable you set at different levels or conditions to observe how the outcome responds. For example, if you’re testing how sunlight affects plant growth, the amount of sunlight is the independent variable—you decide full sun, partial shade, or no light. The plant height after a set period would be the dependent variable, which you measure to see the effect of the sunlight changes. Other factors that could influence growth, like soil type, water, and temperature, are kept constant as controlled variables to ensure any observed differences come from the sunlight manipulation. The term constant isn’t a variable you change; it refers to conditions kept the same. That’s why this option is the best answer—the one you actively manipulate to explore cause-and-effect relationships.