Why is fragment count important in restriction digest?

Correct answer: To verify cut pattern

A restriction enzyme cuts DNA at particular recognition sites. The number of fragments produced depends on how many effective cuts occur and on whether the DNA is linear or circular. Before performing the digest, a restriction map or expected construct usually predicts the fragment pattern. Counting the bands after electrophoresis allows us to compare the observed result with that prediction.

If the fragment count and approximate pattern agree, the digestion is likely complete and the construct may have the expected arrangement. A missing, extra, or unexpected band can indicate incomplete digestion, an incorrect construct, or another experimental problem. Therefore option A is correct: fragment count helps verify the cut pattern. Enzyme colour, water smell, and protein production are unrelated to this verification.