The correct answer is option 2: 2 only.
Statement 1 states that the Tista river flows through Arunachal Pradesh. However, this statement is incorrect. The Tista river does not flow through Arunachal Pradesh.
Statement 2 states that the Tista river falls into the Brahmaputra. This statement is correct. The Tista river is a major tributary of the Brahmaputra river and it merges with the Brahmaputra in Bangladesh.
Therefore, only statement 2 is correct and the correct answer is option 2: 2 only.
The Tista river originates from the Himalayas in Sikkim and flows through West Bengal and Bangladesh. It is an important river in the region and plays a significant role in the agriculture and economy of the areas it passes through.