The Ganga river has the largest river basin in India.

Explanation:
The river basin is the area of land drained by a river and its tributaries. It includes all the land that contributes water to the river. The size of a river basin is determined by the extent of the catchment area and the number and size of the tributaries that flow into the main river.

Here are the reasons why the Ganga river has the largest river basin in India:

1. Geographic extent:
The Ganga river basin covers a vast area in northern India. It spans over 1,080,000 square kilometers, making it the largest river basin in India. It extends across several states, including Uttarakhand, Uttar Pradesh, Bihar, Jharkhand, and West Bengal.

2. Tributaries:
The Ganga river is fed by numerous tributaries, which significantly contribute to its large river basin. Some of the major tributaries of the Ganga include the Yamuna, Son, Gandak, Kosi, and Ghaghara rivers. These tributaries increase the overall drainage area of the Ganga river basin.

3. Population:
The Ganga river basin is home to a significant portion of India's population. Several major cities, including Delhi, Kanpur, Varanasi, and Kolkata, are located along the banks of the Ganga. The dense population in the region also contributes to the large river basin.

4. Agricultural significance:
The Ganga river basin is highly fertile and supports extensive agricultural activities. The alluvial plains formed by the Ganga and its tributaries provide fertile soil for agriculture. The basin is known as the "breadbasket of India" due to its agricultural productivity.

5. Cultural and religious importance:
The Ganga river holds immense cultural and religious significance in India. It is considered a sacred river by Hindus and is worshipped as the goddess Ganga. The river attracts millions of pilgrims and tourists every year, further highlighting its importance and popularity.

In conclusion, the Ganga river has the largest river basin in India due to its extensive geographical coverage, numerous tributaries, high population density, agricultural significance, and cultural importance.