Correct Option
The correct option is (c).
Explanation
The Purvachal hills, also known as the Eastern Hills and Mountains, constitute the eastern extension of the Himalayan range. They are located in Northeast India and run along the boundary between India and Myanmar.
Statement-wise Analysis
- Statement 1 is Correct: The Brahmaputra river marks the easternmost boundary of the Himalayas. Beyond the Dihang gorge, the Himalayas take a sharp bend to the south and spread along the eastern boundary of India. This southward extension is known as the Purvachal.
- Statement 2 is Incorrect: The Purvachal hills spread along the eastern boundary of India, separating it from Myanmar. They do not lie on the western boundary. The range comprises the Patkai Bum, Naga Hills, Manipur Hills, and Mizo or Lushai Hills.
- Statement 3 is Correct: These hills are composed mostly of strong sandstones, which are sedimentary rocks. Due to the heavy rainfall in the region and the nature of the terrain, they are covered with dense forests.
Key Takeaway: The Purvachal hills are the southward extension of the Himalayas formed after the sharp syntaxial bend at the Dihang gorge, running along India's eastern frontier with Myanmar.