Option 1: Wheat

Wheat is not the preferred paint for mixed cropping to enhance the bioavailability of nitrogen. Wheat is a cereal crop commonly grown for its edible grain and is not known for its ability to fix nitrogen in the soil. Nitrogen fixation is the process by which certain plants, such as legumes, convert atmospheric nitrogen into a usable form for plants and other organisms.

Option 2: Gram (chickpea)

Gram, also known as chickpea, is the correct answer. Gram is a legume crop that has the ability to fix nitrogen in the soil. It forms a symbiotic relationship with nitrogen-fixing bacteria in its roots, allowing it to take atmospheric nitrogen and convert it into a form that can be used by plants. This enhances the bioavailability of nitrogen in the soil and benefits other crops grown in the mixed cropping system.

Option 3: Maize

Maize, also known as corn, is not the preferred plant for enhancing nitrogen bioavailability. While maize is a widely grown cereal crop, it is not known for its nitrogen-fixing ability like legume crops such as gram.

Option 4: Barley

Barley is another cereal crop that is not preferred for enhancing nitrogen bioavailability. Similar to wheat and maize