Assertion (A) : Ganga Plain is the most densely-populated part of India. Reason (R) : Ganga is the most harnessed river of India.

The correct answer is Option 2.

Assertion (A) is true because the Ganga Plain, characterized by fertile alluvial soil, flat terrain, and perennial water supply, supports intensive agriculture. This high carrying capacity makes it the most densely populated region in India, housing states like Bihar, West Bengal, and Uttar Pradesh.

Reason (R) is also true. The Ganga is indeed the most harnessed river in India, featuring extensive networks of canals (like the Upper and Lower Ganga Canals) and numerous dams/barrages for irrigation and hydroelectric power.

However, R is not the correct explanation of A. The extreme population density is primarily due to the geographical suitability for agriculture and settlement (topography and climate) rather than merely the technical harnessing of the river. While harnessing supports the population, the fundamental reason for the density is the natural productivity of the plains. Thus, both statements are independent facts.