The state of Andhra was formed in 1953 primarily on the basis of:

The correct answer is: a) Linguistic unity.

Andhra Pradesh was formed in 1953 by merging the Telugu-speaking areas of the erstwhile Madras Presidency and Hyderabad State. The formation of Andhra Pradesh was a result of the Telugu language movement, which sought to create a state for the Telugu people. The movement was successful in achieving its goal, and Andhra Pradesh became the first state in India to be formed on the basis of linguistic unity.

The other options are incorrect because:

• Option b) is incorrect because economic considerations were not the primary factor in the formation of Andhra Pradesh. The state was formed to unite the Telugu people, not to improve the economy of the region.
• Option c) is incorrect because administrative efficiency was not the primary factor in the formation of Andhra Pradesh. The state was formed to unite the Telugu people, not to improve the efficiency of the administration.
• Option d) is incorrect because historical boundaries were not the primary factor in the formation of Andhra Pradesh. The state was formed to unite the Telugu people, not to follow historical boundaries.