The northern plain of India has been formed mainly by the combined depositional work of three major river systems, namely the Indus, the Ganga and which other river?

Introduction / Context:
The northern plain of India is one of the most extensive alluvial plains in the world, supporting dense population and intensive agriculture. It is formed by long term deposition of sediments brought down from the Himalayas and other highlands by major river systems. Standard geography texts describe the plain as the product of three great rivers: the Indus, the Ganga, and a third river that flows through Assam and into Bangladesh.

Given Data / Assumptions:

• The question states that the northern plain has been formed by the Indus, the Ganga, and one more river.
• Options: Brahmaputra, Krishna, Kaveri, and Mahanadi.
• We assume the classic description of the Indo-Gangetic-Brahmaputra plain.
• The river must be part of the Himalayan system and contribute significant alluvium.

Concept / Approach:
The northern plain stretching from Punjab through Uttar Pradesh to West Bengal and Assam is often referred to as the Indo-Gangetic-Brahmaputra plain. The Brahmaputra originates in Tibet, flows through Arunachal Pradesh and Assam, and then enters Bangladesh to join the Ganga (Padma) system. Its enormous sediment load and floodplain deposits are crucial in forming the eastern part of the northern plains. By contrast, Krishna, Kaveri, and Mahanadi are Peninsular rivers and primarily shape the Deccan and east coast regions, not the main northern plain.

Step-by-Step Solution:
Step 1: Recognise that the northern plain is commonly named the Indo-Gangetic-Brahmaputra plain. Step 2: The Indus system shapes the northwestern part of the plain in Punjab and adjoining regions. Step 3: The Ganga system creates the central portion across Uttar Pradesh and Bihar. Step 4: The Brahmaputra system, with its wide floodplains in Assam and Bangladesh, forms the eastern extension of the plain. Step 5: Krishna, Kaveri, and Mahanadi are east or south flowing Peninsular rivers forming deltas and coastal plains, not the northern alluvial belt. Step 6: Thus, the third major river forming the northern plain is the Brahmaputra.

Verification / Alternative check:
Maps in NCERT and other standard textbooks label the great plain of north India as the Indo-Gangetic-Brahmaputra plain. In those diagrams, the Indus and its tributaries occupy the west, the Ganga and its tributaries the centre, and the Brahmaputra the east. No map of this region labels Krishna, Kaveri, or Mahanadi as forming part of the same continuous northern alluvial plain, which confirms that Brahmaputra is the correct answer.

Why Other Options Are Wrong:
Krishna flows through Maharashtra, Karnataka, Telangana, and Andhra Pradesh, shaping the Deccan plateau and parts of the eastern coastal plains. Kaveri flows mainly through Karnataka and Tamil Nadu, forming its delta in the Tamil Nadu coast. Mahanadi flows through Chhattisgarh and Odisha and forms an east coast delta. None of these rivers carve out the giant northern plain associated with the Indus and Ganga systems.

Common Pitfalls:
Sometimes candidates mistakenly focus only on Ganga and Indus and overlook Brahmaputra's role because its plain lies slightly apart in the north east. Others might misinterpret the question and think of any large Indian river, leading to confusion with Mahanadi or Krishna. To avoid this, remember the combined name Indo-Gangetic-Brahmaputra plain and associate it firmly with the northern plain.

Final Answer:
Along with the Indus and the Ganga, the third major river system responsible for forming the northern plain of India is the Brahmaputra river system.