Final answer:
The control group in the radish seedling experiment would be the plants grown under white light, as it serves as the standard condition for comparing the influence of red, blue, and green light on plant growth.
Step-by-step explanation:
In an experiment where radish seedlings were grown in red, blue, green, and white light, the control group would be the group of seedlings grown in white light. This is because white light contains all the wavelengths of the visible spectrum and most resembles natural sunlight, providing a basis for comparison against the other specific light conditions. In scientific experiments, a control group is crucial as it allows researchers to isolate the effect of the independent variable by comparing it with a standard or norm. By using a control group, researchers can determine if the growth effects observed in plants exposed to different colored lights are indeed due to the color of the light or some other factor. In this case, any differences in plant growth under red, blue, or green light can be compared against the growth in white light to understand how specific light spectra influence plant development.