Explanation
1912 is the answer that matches the Bihar-specific fact asked in the question. Bihar was formally separated from Bengal on March 22, 1912, and this date is celebrated as Bihar Diwas (Bihar Foundation Day) every year. Prior to 1912, Bihar was part of the Bengal Presidency under British India. The partition of Bengal in 1905 by Lord Curzon divided Bengal into two parts — East Bengal and West Bengal — but Bihar remained part of Bengal Presidency until 1912. In 1936, Orissa was separated from Bihar to form a separate province. In 1947, India gained independence, and Bihar became a state of independent India. The year 1912 is one of the most important dates in Bihar's administrative history and is frequently asked in all Bihar state-level competitive examinations. Bihar Diwas is observed on March 22 every year with great enthusiasm across the state. In ‘In which year was the state of Bihar formally separated from Bengal?’, the decisive clue is the exact place, institution, event, physical feature or administrative category mentioned in the stem. 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. The alternatives 1905, 1936, 1947 may be valid Bihar-related terms, but they do not satisfy the complete relationship asked here. Revise the complete pair ‘In which year was the state of Bihar formally separated from Bengal? — 1912’ rather than an isolated option letter. This approach improves accuracy in BPSC, Bihar Police, teacher recruitment, SSC, Railway and other examinations while reducing confusion between closely related state facts..