Bihar was separated from Bengal in-

Correct answer: (b) 1912

Explanation

By a proclamation issued on 22 March, 1912, a new province named “Bihar and Orissa” was formed by separating it from the Bengal Presidency, and it came into effect on 1 April 1912. 22 March is celebrated as Bihar Day. On 1 April, 1936, Bihar and Orissa were separated, and both came into existence as separate provinces. The Bihar Public Service Commission considered option (d) as the correct answer to this question.

This explanation is carried over from question 83 of this topic, which the book cross-references.