Answer :
Answer:
Option (4).
Explanation:
Ames test is used to determine the mutagenicity of any substance. The growth of bacteria in a particular chemicals determines the confirm mutagenecity of the chemical.
The his+ reverants are observed in mutagenic control, this may occur due to the reason that some reversion mutation is not caused by which the mutagen has been tested. This reversion mutation may have occur due to some other factors other than the mutagen.
Thus, the correct answer is option (4).