Answer : 4. "Bhupal Singh"
Explanation :

On 18 April 1948, in the third phase of unification of Rajasthan, the princely state of Udaipur merged with the Rajasthan Union and its new name was 'United Rajasthan Union'. In its cabinet formed under the leadership of Manikya Lal Verma, Maharana Bhupal Singh of Udaipur was made the Rajpramukh, Maharao Bhim Singh of Kota was made the senior Deputy Chief.