The correct answer is Fifth.

Hill Area Development Programmes were a crucial initiative undertaken during India's Fifth Five-Year Plan (1974-1979). This plan specifically targeted the development of the hilly regions of the country. The program aimed to address the unique challenges and needs of these areas, including infrastructure development, agricultural improvements, and overall socioeconomic upliftment. Fifteen districts were initially selected for this focused development effort, reflecting the scale and importance of the initiative within the broader national development strategy. The Fifth Five-Year Plan is remembered for its emphasis on poverty alleviation and regional imbalances, of which the Hill Area Development Programmes were a key component. These programs, by focusing on infrastructure, education, and economic opportunities in these previously neglected areas, sought to improve living standards and reduce regional disparities. The implementation was characterized by a multi-pronged approach involving governmental agencies, local communities, and non-governmental organizations. Consequently, the Fifth Five-Year Plan is associated with a significant focus on addressing the developmental needs of India's hilly terrains.