Answer: The correct answer is -
A: beneficial.
Mutation can be described as permanent change in the genetic material (DNA, deoxyribonucleic acid) of living organisms.
In certain genes of bacteria, mutation allows them to become resistant against powerful antibiotics.
Due to this, bacteria are no more sensitive to the action of antibiotics that is they can not be killed by the action of antibiotics.
Thus, such mutation is beneficial to the bacteria as it is increasing the rate of survival of bacteria.
Therefore, option A) is the right answer.