Answer
The biopic that garnered Mammootty the prestigious National Award in 2000 was "Dr. Babasaheb Ambedkar," a captivating portrayal of the life and achievements of the iconic Indian social reformer and architect of the Indian Constitution, Dr. B. R. Ambedkar. Mammootty's exceptional acting brought the essence of Ambedkar's life and struggles to life, showcasing his unwavering dedication to social justice, equality, and the upliftment of the marginalized communities in India.