The correct answer is: C. Hisar
Hisar is a district in the Indian state of Haryana. It is located in the northern part of the state and is bordered by the districts of Jind to the north, Bhiwani to the east, Mahendragarh to the south, and Rewari to the west. The district has a population of over 2 million people and its headquarters is located in the city of Hisar.
Hisar is a major agricultural district and is known for its production of wheat, rice, and cotton. The district is also home to a number of industries, including the manufacture of textiles, machinery, and chemicals.
In terms of mineral resources, Hisar is rich in copper. The district has a number of copper mines, which are operated by the state-owned Hindustan Copper Limited. The copper mines in Hisar are a major source of revenue for the state government.
The other options are incorrect because they are not districts in Haryana that are rich in copper. Mahendragarh is a district in the southern part of Haryana, Karnal is a district in the eastern part of Haryana, and Rewari is a district in the western part of Haryana. None of these districts are known for their production of copper.