The primary source of revenue for Gram Panchayats is:

Property tax
Grants from the state government
Local body tax
Sale of agricultural produce

The primary source of revenue for Gram Panchayats is grants from the state government. This is because Gram Panchayats are local self-government institutions that are responsible for providing basic services to the rural population. The state government provides grants to Gram Panchayats to help them meet their expenses. These grants are used to fund a variety of activities, including construction and maintenance of roads, schools, and hospitals; provision of drinking water and sanitation facilities; and promotion of agriculture and rural development.

Property tax is a tax that is levied on the value of real estate. It is a major source of revenue for local governments, including Gram Panchayats. However, property tax collection is often a challenge for Gram Panchayats, as many people do not pay their taxes.

Local body tax is a tax that is levied on businesses and other commercial establishments. It is another major source of revenue for local governments. However, local body tax collection is also often a challenge for Gram Panchayats, as many businesses do not pay their taxes.

Sale of agricultural produce is not a major source of revenue for Gram Panchayats. This is because most agricultural produce is sold in the open market, and Gram Panchayats do not have a monopoly on the sale of agricultural produce.

In conclusion, the primary source of revenue for Gram Panchayats is grants from the state government.