Option 1: Wheat is not commonly used for green manuring in India. Wheat is a cereal crop that is primarily grown for its grain and is not typically grown specifically for the purpose of green manuring.

Option 2: Sunhemp is the correct answer. Sunhemp, also known as Crotalaria juncea, is a legume plant that is widely used for green manuring in India. It is known for its ability to fix nitrogen in the soil, which helps enrich the soil with this essential nutrient. Sunhemp is a fast-growing plant that produces a large amount of biomass, making it an ideal choice for green manuring.

Option 3: Cotton is not typically used for green manuring in India. Cotton is a cash crop that is grown for its fiber, and it is not commonly grown specifically for green manuring purposes.

Option 4: Rice is also not commonly used for green manuring in India. Rice is a staple food crop in India and is primarily grown for its grain rather than for green manuring.

In conclusion, the correct answer is option 2 - Sunhemp, as it is widely used for green manuring in India due to its nitrogen-fixing properties and high biomass production.