Should be D........
I approached it this way..
Range is always min to max.
X is an unsigned number therefore it should start from zero. Hence Minimum number in our case is Min = 0.
max will be integer part + fractional part..so 2^i - 1 bits + ( fraction part)
binary in fraction is represented as .1111(in case of maximum) which is converted as 1/2 + 1/4 + 1/8 + .. . .....1/f( f bits as mentioned)
it's sum of GP upto finite terms which is 1/2(1-(1/2)^f)/(1- 1/2) we get 1 - 1/2^f.
now max of integral part + max of fractional part.
2^i - 1 + 1 - 1/2^f
= 2^i + 2^f
Finally we get 0 to 2^i + 2^f