India's largest and heaviest rocket is the Geosynchronous Satellite Launch Vehicle (GSLV Mk III), also known as the "Bahubali" rocket. This rocket has a lift-off mass of 640 tonnes and is capable of carrying a payload of up to 4,000 kg to geosynchronous transfer orbit (GTO) or 10,000 kg to low earth orbit (LEO).

The GSLV Mk III is a three-stage rocket that was developed by the Indian Space Research Organisation (ISRO) to meet the country's increasing demand for launching heavy satellites into space. The rocket stands at a height of 43.43 meters and has a diameter of 4 meters. It uses both solid and liquid propulsion systems for its various stages.

The first stage of the GSLV Mk III is powered by two solid rocket boosters (S200) and a liquid-fueled core stage (L110) which uses Vikas engine. The second stage also uses the Vikas engine, and the third stage uses an indigenous cryogenic engine, which was developed by ISRO. The cryogenic engine uses liquid hydrogen as fuel and liquid oxygen as oxidizer. The use of cryogenic engine gives the GSLV Mk III the capability to carry heavier payloads compared to its earlier versions.

The GSLV Mk III has been used for several successful launches, including the Chandrayaan-2 mission, which aimed to land a rover on the moon, and the GSAT-19 communication satellite, which was India's first successful test of its own high-throughput satellite.

In conclusion, the Geosynchronous Satellite Launch Vehicle Mk III is India's largest and heaviest rocket, capable of carrying payloads up to 4,000 kg to GTO and 10,000 kg to LEO. It is a three-stage rocket that uses a combination of solid and liquid propulsion systems and an indigenous cryogenic engine, making it an important tool for India's space exploration and communication endeavors.