Step 1: Understand the Harrod-Domar Model.
The Harrod-Domar growth model links economic growth to the savings rate and capital-output ratio. It emphasizes capital accumulation as the primary driver of growth, making it suitable for a capital-scarce post-independence economy.
Step 2: Match it to the correct Five-Year Plan.
India's First Five-Year Plan (1951-1956) was based on the Harrod-Domar model with a primary focus on agriculture and post-Partition rehabilitation. The Second Plan (1956-61) switched to the Mahalanobis model, which focused on heavy industry.
Step 3: Eliminate the distractors.
The Third Plan used a mixed approach, the Fourth Plan focused on growth with stability, and neither used the Harrod-Domar framework as the base. The First Plan is the clear and well-known answer.
\[ \boxed{\text{First}} \]