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 the remains of marine organisms. It is a major source of calcium carbonate and is used in a variety of industries, including construction, 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 district is home to a number of limestone mines and quarries, which provide employment to a large number of people. Limestone is also used as a building material in the district and is found in a number of historical and religious structures.
The other options are incorrect because they do not have limestone deposits. Idukki is a district in the northern part of Kerala that is known for its tea plantations and hydroelectric projects. Wayanad is a district in the northern part of Kerala that is known for its forests and wildlife. Malappuram is a district in the northern part of Kerala that is known for its textiles and handicrafts.