Explanation:

- The Brahmaputra River is a major river in Asia, flowing through Tibet, India, and Bangladesh.

- In Arunachal Pradesh, the Brahmaputra is referred to as the Dihang. This name is locally used as it enters the Indian state from Tibet.

- Option 1: Tsangpo - It is another name for the Brahmaputra as it flows through Tibet before entering India.

- Option 2: Purab Ganga - This is not a widely recognized name for the Brahmaputra in Arunachal Pradesh.

- Option 3: Dihang - Correct answer. This is the name used in Arunachal Pradesh.

- Option 4: Mandakini - This name typically refers to a tributary of the Ganges, not the Brahmaputra.