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 the state was a result of the Telugu language movement, which had been demanding a separate state for Telugu speakers since the early 20th century. The movement was successful in achieving its goal with the formation of Andhra Pradesh, which was the first state in India to be formed on the basis of linguistic unity.

The other options are incorrect because:

• Option b) Economic considerations is incorrect because the formation of Andhra Pradesh was not primarily motivated by economic considerations.
• Option c) Administrative efficiency is incorrect because the formation of Andhra Pradesh was not primarily motivated by administrative efficiency.
• Option d) Historical boundaries is incorrect because the formation of Andhra Pradesh was not primarily motivated by historical boundaries.