Step 1: Understanding drought-prone areas.
Drought-prone regions are those that frequently experience water scarcity and low rainfall over long periods of time.
Step 2: Analyzing the options.
Assam: Receives heavy rainfall and is not drought-prone.
West Bengal: Has moderate to heavy rainfall.
Kerala: Also receives abundant rainfall.
Gujarat: Lies in a semi-arid region and frequently faces drought conditions, especially in Kutch and Saurashtra areas.
Step 3: Conclusion.
Hence, the most drought-prone state among the given options is Gujarat.