The correct answer is (c), paddy.
Blue-green algae are a type of bacteria that can fix nitrogen from the atmosphere. This means that they can convert nitrogen gas into ammonia, which is a form of nitrogen that plants can use. Paddy is a type of rice that is grown in flooded fields. The flooded fields provide an ideal environment for blue-green algae to grow. As a result, blue-green algae are often used to supply nitrogen to paddy fields.
Bajra is a type of millet that is grown in dry areas. Maize is a type of corn that is grown in both dry and wet areas. Wheat is a type of cereal that is grown in dry areas. These crops do not require as much nitrogen as paddy, so blue-green algae are not typically used to supply nitrogen to them.
Blue-green algae are a valuable source of nitrogen for paddy fields. They can help to improve crop yields and reduce the need for fertilizer. However, it is important to note that blue-green algae can also produce toxins that can be harmful to humans and animals. Therefore, it is important to monitor blue-green algae populations in paddy fields and to take steps to prevent the growth of toxic algae blooms.