As per 2011 census, the district having the lowest literacy rate among the districts of Assam is :

​The importance of the 2011 census- The 2011 census was conducted in two phases- House listing and Population enumerating. It was also the first time biometrics information has been recorded. There has been a visible growth in population and adult literacy rate in India. IMPORTANT POINT- Below given is the literacy percentage of the given districts of Assam in order of highest to lowest- DISTRICT LITERACY PERCENTAGE DHUBR 58.34% CHIRANG 63.55% UDALGURI 65.41% DIMA HASAO 77.54% Therefore the answer is Option 2, Dhubur.