Assam's Surma Valley (now partly in Bangladesh) had Muslim-majority population. On the eve of partition, hectic activities intensified by the Muslim League as well Congress with the former having an edge. A referendum had been proposed for Sylhet Region (now mostly in Bangladesh). Mazumdar along with Basanta Kumar Das (then Home Minister of Assam) travelled throughout the valley organising the Congress and addressing meetings educating the masses about the outcome of partition on the basis of religion. On 20 February 1947, Mazumdar inaugurated a convention – Assam Nationalist Muslim's Convention at Silchar. There after another big meeting was held at Silchar on 8 June 1947. Both the meetings, which were attended by a large section of Muslims, paid dividend. He was also among the few who were instrumental in retaining the Barak Valley region of Assam, especially Karimganj with India. Mazumdar was the leader of the delegation that pleaded before the Radcliffe Commission that ensured that a part of Sylhet, the present Karimganj district, remained with India.. Arun Kumar Chanda did not join Bordoloi cabinet in 1946 but preferred to do social work as a legislator and also to uplift the premier educational institution, G.C. College. Unfortunately he soon died leaving a huge vacuum of an able Bengali Hindu leader with a secular bent of mind.