In an experiment, which group is expected to yield no positive result under the tested conditions?

• A. Negative control
• B. Positive control
• C. Experimental sample
• D. Control group

Answer: (A)

A negative control is designed to show what the system looks like without the experimental variable, so it should produce no positive signal under the tested conditions. This baseline helps confirm that any positive result seen in the other samples is due to the variable being tested, not contamination, background noise, or a procedural error. If the negative control showed a positive result, it would indicate something is producing the signal on its own, which would call into question the validity of the experiment. By contrast, a positive control is expected to yield a known positive outcome to show the assay can detect the effect, the experimental sample is what’s being tested for the effect, and a control group is a general term for a baseline reference group.