Question

the variable a scientist manipulates in an experiment is called the observation variable controlled variable dependent variable independent variable

Explanation:

In experimental design (a concept in Natural Science, specifically in scientific method), the independent variable is the one the scientist manipulates to observe changes in other variables. Observation variable is not a standard term, controlled variables are kept constant, and dependent variables are the ones observed/measured (depend on the independent variable). So the variable manipulated is the independent variable.

Answer:

independent variable (the option with "independent variable" text, likely the red - colored option in the image)