The correct answer is option 2, the Survey of India.

The Survey of India is the oldest scientific department of the Government of India. It was established in 1767 and is responsible for conducting topographic mapping and surveying throughout the country. The department plays a crucial role in providing accurate and up-to-date maps, charts, and geospatial information for various purposes including defense, infrastructure development, disaster management, and resource planning.

Option 1, the Department of Biotechnology, is not the oldest scientific department of the Government of India. It was established in 1986 and is primarily responsible for promoting and coordinating biotechnology-related activities in the country.

Option 3, the India Meteorological Department, is an important scientific department but it is not the oldest. It was established in 1875 and is responsible for weather forecasting, climate monitoring, and providing other meteorological services.

Option 4, DRDO (Defence Research and Development Organisation), is a government agency responsible for military research and development in India. While it is an important scientific department, it is not the oldest. DRDO was established in 1958.

Therefore, the correct answer is option 2, the Survey of India.