The driest area of Himachal Pradesh is

Spiti
Una
Chamba
Dharamshala

The correct answer is A. Spiti.

Spiti is a cold desert located in the Lahaul and Spiti district of Himachal Pradesh, India. It is one of the driest and coldest inhabited places in the world. The average annual rainfall in Spiti is only 100 mm, and the temperature can drop to -40 degrees Celsius in winter.

The other options are not as dry as Spiti. Una is a district in Himachal Pradesh that is known for its hot springs and temples. Chamba is a district in Himachal Pradesh that is known for its scenic beauty and temples. Dharamshala is a town in Himachal Pradesh that is known for its Buddhist monasteries and as the winter home of the Dalai Lama.