How are restriction enzymes named?

The correct answer is Option (2) → First letter from the genus and two letters from the species of the organism

Restriction enzymes are named after the bacterium from which they were isolated. The first letter comes from the genus and the next two letters from the species. In EcoRI, “E” is from Escherichia and “co” from coli; “R” comes from the strain RY 13. The Roman numeral at the end shows the order in which enzymes were isolated from that strain, so EcoRI was the first one found.

NCERT Extract:
Restriction Enzymes – “… The convention for naming these enzymes is the first letter of the name comes from the genus and the second two letters come from the species of the prokaryotic cell from which they were isolated, e.g., EcoRI comes from Escherichia coli RY 13. In EcoRI, the letter ‘R’ is derived from the name of strain. Roman numbers following the names indicate the order in which the enzymes were isolated from that strain of bacteria.”