In Tibet the river known locally as Tsangpo is called by what name after it enters India?

Introduction / Context:
Many major rivers flow across international borders and are known by different local names in different regions. Understanding these name changes is an important part of physical geography. The river called Tsangpo in Tibet is a prominent example that later becomes one of the great rivers of India and Bangladesh.

Given Data / Assumptions:

- The river name given is Tsangpo, as used in Tibet. - The question asks what this river is called in India, after it crosses the border. - The options are Kosi, Gandak, Brahmaputra and Ganga. - We assume knowledge of major Himalayan river systems.

Concept / Approach:
The river originates in the Tibetan plateau as the Yarlung Tsangpo. It flows eastwards across Tibet and then takes a sharp turn, entering India through Arunachal Pradesh. After entering India, it is known as the Brahmaputra. The river then flows through Assam and eventually enters Bangladesh, where it is called the Jamuna and later merges with the Ganga river system. Thus the correct Indian name corresponding to Tsangpo is Brahmaputra.

Step-by-Step Solution:
Step 1: Recall that the Yarlung Tsangpo is frequently mentioned as a trans boundary river originating in Tibet. Step 2: Remember that it enters India in the eastern Himalayas and becomes the Brahmaputra in Arunachal Pradesh and Assam. Step 3: Note that Kosi and Gandak are other important Himalayan rivers but originate in Nepal, not as Tsangpo in Tibet. Step 4: Ganga is a separate major river system arising mainly from the Gangotri glacier region and is not simply a renaming of Tsangpo. Step 5: Therefore, select Brahmaputra as the correct correspondence to Tsangpo.

Verification / Alternative check:
School and competitive exam geography books typically include a table of important rivers with their names in different regions. In that table, the sequence Yarlung Tsangpo in Tibet, Brahmaputra in India and Jamuna in Bangladesh is clearly presented. Maps of the Brahmaputra basin also label the Tibetan stretch as Tsangpo, confirming that they refer to the same river system with changing names across borders.

Why Other Options Are Wrong:
Kosi is a trans boundary river between Nepal and India and is sometimes called the Sorrow of Bihar, but it is not the same river as Tsangpo. Gandak similarly originates in Nepal and flows into India as a tributary of the Ganga, not as a continuation of Tsangpo. Ganga is another great river of northern India but arises from different headwaters and is not simply the downstream name of Tsangpo.

Common Pitfalls:
A frequent mistake is to treat all major Himalayan rivers as interchangeable and to guess Ganga because it is the most famous. Another pitfall is confusion between names like Tsangpo and Indus, which also cross international borders with multiple local names. To avoid such errors, it is useful to memorise a few classic examples such as Tsangpo becoming Brahmaputra and Huang He being called the Yellow River, instead of mixing them up.

Final Answer:
The river known as Tsangpo in Tibet is called the Brahmaputra after it enters India.