The Lohit River is a tributary of which of the following major Himalayan rivers?

Correct — B. NCERT's Class XI text India: Physical Environment traces the Brahmaputra into India as the Siang, or Dihang, west of Sadiya in Arunachal Pradesh.

Flowing south-west, it receives its main left-bank tributaries, the Dibang and the Lohit, and thereafter is called the Brahmaputra. The Lohit feeds the Brahmaputra → option (b).

Why the others are wrong

• (a)
  Ganga — The Ganga gathers rivers such as the Yamuna, Gandak and Kosi across the northern plain. The Lohit joins the Siang in the far north-east, in the Brahmaputra system.
• (c)
  Indus — The Indus drains the western end of the Himalaya and empties into the Arabian Sea east of Karachi. The Lohit belongs to the opposite, eastern end.
• (d)
  Yamuna — The Yamuna is itself a tributary, the longest of the Ganga, meeting it at Prayag (Prayagraj). It flows nowhere near Arunachal Pradesh.

The Brahmaputra rises near Mansarovar lake and runs east through southern Tibet as the Tsangpo. It cuts a deep gorge near Namcha Barwa and enters India as the Siang.

After the Dibang and the Lohit join it, it crosses the Assam valley, taking the Subansiri, Kameng, Manas and Sankosh from the right bank.

The Lohit itself rises in Tibet, where it is the Zayul Chu, and crosses the Mishmi Hills.

Key facts

• NCERT: the Siang (Dihang) receives the Dibang and the Lohit, and is thereafter called the Brahmaputra.
• The Brahmaputra is called the Tsangpo in southern Tibet.
• The Dhola–Sadiya Bridge, also called the Bhupen Hazarika Setu, spans the Lohit between Assam and Arunachal Pradesh.
• The Brahmaputra enters Bangladesh near Dhubri.

Common traps

• Choosing the Ganga as the default Himalayan river. The Lohit lies in the Brahmaputra system of the far north-east.
• Mixing up banks: the Dibang and the Lohit join from the left, the Subansiri and the Manas from the right.

No directly related past PYQ was found.