Answer : 1. "50 cm"
Explanation :

1. The 50 cm parallel rainfall line parallel to Aravali (desert and non-desert) divides Rajasthan into two parts.

2. The eastern boundary of the 'Western Sandy Plains' in western Rajasthan forms the 25 cm isobar line.

3. The 25 cm isobar line dividing the sandy dry plains and the semi-arid transitional plain is climatic.

4. The western belt which is the 'vast desert', covered with sand dunes, extends from the Great Rann (Ran of Kutch) to Punjab along the Pakistan border.