The correct answer is option 1: 1 km starting from their demarcated boundaries. The Supreme Court of India has directed that every protected forest, national park, and wildlife sanctuary should have a mandatory eco-sensitive zone (ESZ) of at least 1 km from their demarcated boundaries.

An eco-sensitive zone is an area around a protected area aimed at conserving the wildlife, habitats, and biodiversity in the vicinity. It acts as a buffer zone to minimize the negative impacts of human activities on the protected areas and helps in preserving the ecological balance.

By implementing this directive, the Supreme Court aims to protect the fragile ecosystems and biodiversity found in these protected areas. This will help in preventing encroachments, illegal activities, deforestation, and pollution that could harm the flora and fauna. It will also help in maintaining the integrity of the protected areas and ensuring their long-term conservation.

It is important to note that while the mandatory minimum eco-sensitive zone is set at 1 km, individual states or regions may choose to designate larger areas as eco-sensitive zones based on their specific requirements and environmental considerations.