The correct answer is option 'C', Himachal.

The Lesser Himalayas are known as Himachal. Let's delve deeper into this answer and understand why Himachal is the correct option.

The Lesser Himalayas:
- The Lesser Himalayas, also known as the Outer Himalayas or the Sub-Himalayan Range, is a mountain range in the northern part of India.
- It is a parallel range to the Greater Himalayas and lies to the south of it.
- The Lesser Himalayas extend from Jammu and Kashmir in the west to Arunachal Pradesh in the east, covering several Indian states such as Himachal Pradesh, Uttarakhand, Sikkim, and parts of northeastern states.
- This mountain range is an important part of the Himalayan system and plays a significant role in shaping the geography and climate of the region.

Himachal:
- Himachal, also known as Himachal Pradesh, is a state in northern India that is located in the western part of the Lesser Himalayas.
- The name "Himachal" is derived from the Sanskrit words "Hima" (meaning snow) and "Achal" (meaning mountain).
- Himachal is known for its picturesque landscapes, snow-capped mountains, lush valleys, and charming hill stations.
- It is a popular tourist destination and is often referred to as the "Devbhumi" or "Land of the Gods" due to its numerous temples and religious sites.
- The state is known for its rich cultural heritage, warm hospitality, and adventure tourism activities like trekking, skiing, and paragliding.

Other Options:
- Option 'A', Himadri, is not the correct answer. Himadri is a term that refers to the Greater Himalayas, which is the highest and most prominent range in the Himalayan system.
- Option 'B', Purvanchal, refers to the easternmost region of India, which includes states like Bihar, Jharkhand, Odisha, and West Bengal. It is not related to the Lesser Himalayas.
- Option 'D', Shivaliks, is also an incorrect answer. The Shivalik Hills, or Shivaliks, are the southernmost range of the Lesser Himalayas. They are located in northern India and extend from the state of Jammu and Kashmir to the Indian state of Haryana.

In conclusion, the Lesser Himalayas are known as Himachal. This term refers to the state of Himachal Pradesh, which is located in the western part of the Lesser Himalayas.