The correct answer is: A. Kerala
Kerala was the first state in India to constitute a green bench in 1996. The green bench is a special bench of the Kerala High Court that deals with environmental issues. The bench was constituted in response to the increasing environmental degradation in the state. The green bench has played a significant role in protecting the environment in Kerala. It has issued several orders and directions to the government and other authorities to prevent environmental pollution and degradation. The green bench has also been instrumental in promoting environmental awareness and education in the state.
The other options are incorrect. Tamil Nadu constituted a green bench in 2001, Assam constituted a green bench in 2002, and Madhya Pradesh constituted a green bench in 2003.