The correct answer is option 1: "It is a multi-barrel rocket system."

Option 1 correctly identifies Pinaka as a multi-barrel rocket system. This means that Pinaka is a type of artillery weapon that fires multiple rockets simultaneously from a single platform. This system is designed to provide a high volume of fire in a short period of time, allowing it to be used for rapid and intense attacks against enemy positions.

Option 2 is incorrect as Pinaka is not a type of battle tank. Battle tanks are armored vehicles used in ground combat, armed with heavy firepower and strong defense.

Option 3 is also incorrect as Pinaka is not an advanced submarine. Submarines are underwater vessels used for various purposes, such as surveillance, warfare, and transportation.

Option 4 is incorrect as well. Pinaka is not an indigenously developed drone system. Drones are unmanned aerial vehicles that can be used for various purposes, such as surveillance, reconnaissance, and targeted strikes.

In conclusion, Pinaka is correctly identified as a multi-barrel rocket system, specifically designed for delivering a high volume of fire.