Correct Answer: Second Five-Year Plan

Solution : The correct answer is (b) Second Five-Year Plan.

The concept of "mixed economy" was introduced in India during the Second Five-Year Plan (1956-61). The Second Five-Year Plan was based on the Mahalanobis model of development, which emphasized the development of basic and heavy industries as the driving force of economic growth. The model also called for a mixed economy, with a significant role for both the public and private sectors.

The concept of mixed economy has been a cornerstone of India's economic policy ever since. The Indian government has played a significant role in the development of the economy, but it has also allowed the private sector to play a major role. This has helped to create a more balanced and sustainable economy.