Step 1: Understanding the Concept.
A Savarna Aayog is meant to identify poor and disadvantaged families within upper (forward) castes, so that welfare support can reach them despite their caste not being an officially backward category.
Step 2: Check the options.
Uttar Pradesh, Madhya Pradesh, and Rajasthan did not set up this particular commission, so options A, C, and D are wrong.
Step 3: Final Answer.
The Bihar government set up the Savarna Aayog, so option B is correct.