Which princely state was the only Muslim-majority state in the Punjab region?

The correct answer is: a) Malerkotla.

Malerkotla was a princely state in the Punjab region of British India. It was the only Muslim-majority state in the region. The state was founded in 1661 by Nawab Sher Mohammed Khan, a Mughal nobleman. The state was ruled by the Nawabs of Malerkotla until it was merged with the Indian Union in 1947.

The other options are incorrect because they are not Muslim-majority states. Bahawalpur is a Muslim-majority state in Pakistan, but it is not located in the Punjab region. Loharu is a Hindu-majority state in Haryana, India. Khairpur is a Muslim-majority state in Sindh, Pakistan.