In negative control of transcription by the lac operon, how does the presence of an inducer affect transcription?

a) the inducer prevents the repressor from binding to the operator
b) the inducer binds to the operator
c) the inducer causes the repressor to bind to the operator
d) the inducer does not bind to the operator

The correct answer is a) the inducer prevents the repressor from binding to the operator

Explanation:

In lac operon lac I gene synthesize repressor protein that binds to the operator region of the lac operon and inhibits the transcription of the mRNA  by partially blocking the promotor region of lac operon where RNA polymerase binds.

When the inducer is present it binds to the repressor protein and makes a conformation change in the protein as a result repressor protein is not able to bind the operator region of the operon and do not able to block the transcription of the lac operon.

Therefore in the presence of inducer transcription of operon occurs so the right answer is a) the inducer prevents the repressor from binding to the operator.