Karpoori Thakur is the answer that matches the Bihar-specific fact asked in the question. oori Thakur is popularly known as Jan Nayak. The key to this question is the precise association expressed in its wording: “Which Bihar leader was popularly known as 'Jan Nayak'?” The answer Karpoori Thakur matches that clue directly and is therefore factually appropriate. Option A — Jayaprakash Narayan — is incorrect because it does not match the exact person, district, location, institution, river, event or identifying feature required by the question. It may be associated with another Bihar-related context, but that broader association does not satisfy this specific wording. Option C — Sri Krishna Sinha — is incorrect because it does not match the exact person, district, location, institution, river, event or identifying feature required by the question. Option D — Anugrah Narayan Sinha — is incorrect because it does not match the exact person, district, location, institution, river, event or identifying feature required by the question. Bihar GK questions frequently place neighbouring districts, related historical personalities, nearby rivers or institutions from the same field among the options. Karpoori Thakur is popularly known as Jan Nayak. Bihar GK questions frequently place neighbouring districts, rivers, historical centres, personalities or government institutions together as distractors, so recognition of a familiar name alone is insufficient.