Which one of the following rivers is not a tributary of river Brahmaputra?

The Brahmaputra river system is characterized by numerous Himalayan tributaries. Major right-bank tributaries include the Subansiri, Kameng, Manas, and Sankosh [1]. The Subansiri is an antecedent river originating in Tibet, while the Manas and Kameng are also significant northern tributaries that join the Brahmaputra in the Assam valley [3]. In contrast, the Mahananda is a major tributary of the Ganga river system [4]. It originates in the Darjeeling hills and joins the Ganga in West Bengal/Bangladesh, serving as one of the principal northern bank tributaries of the Ganga alongside the Yamuna, Ghaghra, and Kosi [4]. Therefore, while Manas, Kameng, and Subansiri are integral parts of the Brahmaputra drainage, the Mahananda belongs to the Ganga system [3].

Sources

1. [1] INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.) > Chapter 3: Drainage System > The Brahmaputra System > p. 23
2. [2] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 3: The Drainage System of India > The Subansiri River > p. 17
3. [3] https://knowindia.india.gov.in/profile/rivers.php
4. [4] https://indiawris.gov.in/wiki/doku.php?id=ganga