The correct option is D 35
Given : Mohan is 18th from either end of a row => Mohan is in 18th position from both top & bottom of the row or left end & right end of a row
Hence we can conclude that 17 boys are before Mohan and 17 boys are after Mohan in the row.
Therefore, the total no: of students =17+1(Mohan)+1=35
Hence, option 'D' is correct.