What are bacteriophages ?

Viruses that infect bacteria .

The correct answer is Option (2) -Viruses that infect bacteria.

Bacteriophages, or simply "phages," are a type of virus that specifically target and infect bacterial cells. They attach to the surface of a bacterium, inject their genetic material (either DNA or RNA), and use the bacterial machinery to replicate themselves. Eventually, new phages are produced inside the bacterium, often causing the bacterial cell to burst (lyse), releasing the new phages to infect other bacteria.

Bacteriophages are widely studied in genetics and molecular biology and are used in research and therapeutic applications to combat bacterial infections.