Assertion: Pili are tubular structures present in bacteria which help in conjugation.

Reason: Formation of pili is controlled by F+ or fertility factor.

The correct option is A Both assertion and reason are true and reason is the correct explanation of assertion
Cells carrying the F plasmid (fertility factor) promote the synthesis of pili (singular, pilus) on the bacterial cell surface. Pili are minute proteinaceous tubules that allow the F⁺ cells to attach to other cells and maintain contact with them; that is, to conjugate.