Why was Mountbatten's Plan finally accepted by the Congress?

(1) The COMMUNAL VIOLENCE that had followed Direct Action Day in 1946 had spread across Bengal, Bihar and Punjab, and the Congress concluded that partition was the only way to stop the killing and avoid a civil war. (2) The League’s obstruction inside the Interim Government had shown that a united India with an unwilling partner would be unworkable. A SMALLER INDIA WITH A STRONG CENTRE was judged better than a larger one with a weak centre, and further delay risked the disintegration of the country.

One mark each, argued from the CONGRESS point of view — the question asks why they accepted, not what the plan contained. The "smaller India with a strong Centre" argument is the reasoning Nehru and Patel actually used and is the one examiners look for. One closing line adds balance: Gandhiji opposed partition to the last, so the decision divided the Congress itself.