Which National Curriculum Framework (NCF) recommended Environmental Studies to be taught as an integrated curricular area at the primary level?

The correct option is NCF–1975.

Explanation:
The National Curriculum Framework (NCF) 1975, titled "The Curriculum for the Ten-Year School: A Framework", recommended that Environmental Studies should be taught as an integrated subject at the primary school level. It proposed that in the first two years (Classes I and II), Environmental Studies should look at both the natural and social environments together, while in Classes III to V, it would be split into Environmental Studies I (Natural Sciences) and Environmental Studies II (Social Sciences).

Therefore, the NCF–1975 was the first framework to recommend Environmental Studies as an integrated curricular area for primary classes.