The correct answer is option 3: Light combat aircraft.

Option 1: Main battle tank - A main battle tank is a heavily armored combat vehicle designed for front-line combat. This is not the correct answer because Tejas is not a main battle tank.

Option 2: Nuclear submarine - A nuclear submarine is a submarine powered by a nuclear reactor. This is not the correct answer because Tejas is not a nuclear submarine.

Option 3: Light combat aircraft - Tejas, the name mentioned in the question, refers to a light combat aircraft. It is a single-seat, single-engine, multirole fighter jet developed by the Aeronautical Development Agency (ADA) in India. It is designed and manufactured domestically, and it is one of the smallest and lightest aircraft in its class. Tejas is used by the Indian Air Force and the Indian Navy. This is the correct answer.

Option 4: Aircraft carrier - An aircraft carrier is a warship that serves as a seagoing airbase, equipped with a deck for launching and recovering aircraft. This is not the correct answer because Tejas is not an aircraft carrier.

In conclusion, Tejas is the name of a light combat aircraft.