The correct answer is: A. Sonipat
Sonipat is the largest producer of iron pipes in Haryana. It is located in the northern part of the state, and is one of the most industrialized districts in Haryana. The district has a number of iron and steel mills, which produce a variety of products, including iron pipes.
Gurugram is the second largest city in Haryana, and is located in the southern part of the state. It is a major financial and technology hub, and is home to a number of multinational companies. However, Gurugram does not have a significant iron and steel industry.
Faridabad is another major city in Haryana, and is located in the southern part of the state. It is a major industrial hub, and is home to a number of iron and steel mills. However, Faridabad is not the largest producer of iron pipes in Haryana.
Hisar is located in the northern part of Haryana, and is a major agricultural and educational hub. It does not have a significant iron and steel industry.
Therefore, the correct answer is: A. Sonipat