Correct Answer:
B. October 1905
The correct answer is October 1905. The Partition of Bengal was announced on 19 July 1905 and formally came into effect on 16 October 1905. The partition was carried out by Lord Curzon, the then Viceroy of India, on administrative grounds. The province of Bengal was divided into two provinces: Western Bengal (including Bihar and Orissa) with its capital at Calcutta, and Eastern Bengal and Assam with its capital at Dhaka. The partition sparked widespread protests across India, leading to the Swadeshi Movement. The option August 1905 is incorrect because the partition was not implemented in that month. November 1905 and December 1905 are also incorrect. Therefore, October 1905 is the correct date when the partition formally came into effect.