In which year, did the ‘Indian Education Commission’ (The sixth commission in the history of Indian Education) under the chairmanship of Dr. D S. Kothari submit its report?

The correct option is 1966.

The Indian Education Commission, popularly known as the Kothari Commission, was constituted by the Government of India on July 14, 1964, under the chairmanship of Dr. Daulat Singh Kothari (D. S. Kothari), who was then the chairman of the University Grants Commission (UGC).
The commission was set up to examine all aspects of the educational sector in India, from primary to university level, and to advise the government on a standardized pattern of education.
After rigorous research and consultations spanning nearly two years, the Commission submitted its final comprehensive report, titled "Education and National Development", on June 29, 1966.