Population density (people per square km) is highest in:

The correct answer is: The Kaveri Delta.

The Kaveri Delta is a region in the Indian state of Tamil Nadu. It is located in the southeastern part of the state, on the Bay of Bengal. The delta is formed by the Kaveri River, which is one of the longest rivers in India. The Kaveri Delta is a very fertile region, and is home to a large population. The population density of the Kaveri Delta is about 1,000 people per square kilometer.

The other options are incorrect for the following reasons:

• Coastal districts: The population density of coastal districts is not as high as the population density of the Kaveri Delta. This is because coastal districts are often less fertile than inland areas.
• The Western Ghats: The population density of the Western Ghats is also not as high as the population density of the Kaveri Delta. This is because the Western Ghats are a mountain range, and are not as suitable for agriculture as lowland areas.
• Dry interior districts: The population density of dry interior districts is the lowest of all the options. This is because dry interior districts are often not as fertile as other areas, and are also more prone to drought.