What is an operon?

Wild type $E. coli$ cells are growing in a normal medium with glucose. They are transferred to a medium containing only lactose as the sugar. Which one of the following changes takes place?

Which of the following statements concerning the regulatory gene $(i)$,associated with the $lac$ operon are incorrect?
$(I.)$ $\text{mRNA}$ is transcribed from the $i$ gene whether lactose is present or not.
$(II.)$ $\text{mRNA}$ is transcribed from the $i$ gene only when the lactose is present.
$(III.)$ $\text{mRNA}$ is transcribed from the $i$ gene only when the lactose is not present.
$(IV.)$ Lactose inhibits the translation of $i$ gene $\text{mRNA}$.

Which of the following is a regulatory gene?

Select the correct option for $\beta$-galactosidase.

What does the given figure represent?