The correct answer is b) Palakkad.
Limestone deposits are found in the Palakkad district of Kerala. The district is located in the central part of the state and is known for its rich mineral resources. Limestone is a sedimentary rock that is formed from the accumulation of calcium carbonate. It is used in a variety of industries, including construction, cement manufacturing, and agriculture.
The limestone deposits in Palakkad are of high quality and are considered to be some of the best in the country. The deposits are located in the foothills of the Western Ghats and are estimated to be over 100 million years old. The limestone is quarried and processed at a number of factories in the district.
The limestone industry is a major contributor to the economy of Palakkad. The industry employs thousands of people and generates significant revenue for the state government. The limestone deposits in Palakkad are a valuable resource that is essential to the development of the district.
The other options are incorrect because they are not districts of Kerala. Idukki is a district in the northern part of the state, Wayanad is a district in the north-central part of the state, and Malappuram is a district in the northern part of the state.