Which statement best describes a positive control in chemical testing?

Which statement best describes a positive control in chemical testing?

• A. Both controls yield the same result
• B. Positive control yields expected result to show test works
• C. Controls are unnecessary in simple tests
• D. Negative control yields no result to detect contamination or drift

Answer: (B)

A positive control shows the test system can produce a positive result when the target is present. By including a sample that is known to be positive, you verify that the reagents, instruments, and procedures are working correctly. This confirmation lets you trust the results from unknown samples, because you’ve demonstrated the assay can detect the target as intended. If the positive control fails to give the expected positive signal, you know the test isn’t reliable and you’d troubleshoot before drawing conclusions about unknowns.

The idea that both controls yield the same result isn’t right because the positive control should be positive while the negative control should show no signal, allowing you to distinguish true positives from background. Controls are essential even in simple tests—they validate that the assay is functioning. The statement about the negative control yielding no result to detect contamination or drift describes the role of the negative control, but it doesn’t define what a positive control does.