The correct answer is: Oil refineries.
Jamnagar is a city in the Indian state of Gujarat. It is the headquarters of Jamnagar district and the seventh-largest city in Gujarat. The city is located on the Gulf of Kutch, about 320 kilometers (200 mi) from the state capital, Gandhinagar.
Jamnagar is known for its large-scale oil refineries. The city is home to the world’s largest oil refinery, the Jamnagar Refinery, which is operated by Reliance Industries. The refinery has a capacity of 1.24 million barrels per day (200,000 m3/d) and is one of the largest refineries in the world.
In addition to oil refineries, Jamnagar is also home to a number of other industries, including petrochemicals, textiles, and pharmaceuticals. The city is also a major port and is connected to other parts of India by road, rail, and air.
The other options are incorrect because:
- Textile mills are not a major industry in Jamnagar.
- Diamond cutting units are located in Surat, another city in Gujarat.
- Shipbuilding yards are located in Mumbai, another city in India.