Which step in the scientific method involves testing a hypothesis under controlled conditions?

• A. Observation
• B. Hypothesis
• C. Analysis
• D. Experiment

Answer: (D)

Testing a hypothesis under controlled conditions is the experiment step. This is where you deliberately manipulate the independent variable and observe the effect on the dependent variable while keeping other factors constant to minimize confounding influences. This controlled setup lets you determine cause-and-effect relationships and produce data you can analyze to see whether the results support or refute the hypothesis. For example, to see if a nutrient boosts plant growth, you would provide different nutrient levels but keep light, water, soil type, and temperature the same, then measure growth over time. Observation gathers what you notice, a hypothesis is an educated guess you plan to test, and analysis interprets the collected data after the test.