The correct option is 1 only
Explanation
The Southwest Monsoon approaches the Indian landmass in two distinct branches: the Arabian Sea branch and the Bay of Bengal branch. The trajectory of the Bay of Bengal branch is significantly influenced by the topography of the Arakan Yoma mountains and the Himalayas.
Statement 1 is Correct: The Bay of Bengal branch strikes the coast of Myanmar and parts of southeast Bangladesh. However, the Arakan Yoma mountains deflect a large portion of this branch towards the Indian subcontinent. Consequently, the monsoon winds enter West Bengal and Bangladesh from the south and southeast direction.
Statement 2 is Incorrect: This branch does not avoid the Brahmaputra valley. Instead, it splits, with one sub-branch moving northward to strike the Garo, Khasi, and Jaintia hills, causing heavy rainfall (e.g., in Cherrapunji and Mawsynram). These winds subsequently enter and travel through the Brahmaputra valley.
Statement 3 is Incorrect: The second sub-branch moves westward (not eastward) along the Ganga plains, traveling up the river valley towards the thermal low in northwest India. It passes through Bihar and Uttar Pradesh and eventually reaches the Punjab and Haryana plains, where it merges with the Arabian Sea branch. It does not terminate in Bihar.
Key Takeaway: The Bay of Bengal branch enters the Indian mainland from the south/southeast due to deflection by the Arakan Yoma and splits into two streams: one entering the Brahmaputra valley and the other advancing westward along the Ganga plains.