The district known for its cashew industry is:

Kannur
Kollam
Kasaragod
Palakkad

The correct answer is: A) Kannur.

Kannur is a district in the Indian state of Kerala. It is the northernmost district of Kerala and is known for its cashew industry. The district is home to over 100 cashew factories and employs over 100,000 people in the cashew industry. The cashew industry is a major contributor to the economy of Kannur district.

The other options are incorrect. Kollam is a district in the Indian state of Kerala. It is known for its backwaters and beaches. Kasaragod is a district in the Indian state of Kerala. It is known for its forests and wildlife. Palakkad is a district in the Indian state of Kerala. It is known for its tea plantations.