In the $lac$ operon, what does the term "$lac$" refer to?

The functional complex that consists of a cluster of genes including structural genes,a promoter gene,an operator gene,and a regulator gene was discovered by:

$A$ gene that is responsible for the synthesis of a polypeptide chain is called a .......

In an inducible operon, the genes are

The switching on and off of the $lac$ operon is regulated by which of the following?

Structural gene is monocistronic $- P$
Structural gene is polycistronic $- Q$
Select the correct option for $P$ and $Q$.
$\quad\quad\quad P \quad\quad Q$