Who were the first to explain the lac operon model?

The correct answer is Option (2) → Francois Jacob and Jacque Monod

The lac operon was worked out by Francois Jacob, a geneticist, and Jacque Monod, a biochemist. They were the first to explain a transcriptionally regulated system. In their model, a polycistronic structural gene in E. coli is regulated by a common promoter and regulatory genes, an arrangement called an operon.

NCERT Extract:
The Lac Operon – “The elucidation of the lac operon was also a result of a close association between a geneticist, Francois Jacob and a biochemist, Jacque Monod. They were the first to elucidate a transcriptionally regulated system. In lac operon (here lac refers to lactose), a polycistronic structural gene is regulated by a common promoter and regulatory genes. Such arrangement is very common in bacteria and is referred to as operon.”