Detailed Solution:
The correct answer is “Make its water pollution free only”.
The main purpose of the "Ganga Action Plan" (GAP), launched in 1985 by the Government of India, was primarily to make its water pollution free. This initiative aimed to address the deteriorating water quality of the Ganga River due to increasing pollution from industrial waste, domestic sewage, and other sources.
The project involved various measures like sewage treatment, waste management, and public awareness campaigns to restore the river's ecological balance.