None of the answers are correct.
Yes, the MVT applies to the function on the interval [1 , 5] since the square root function is continuous on the closed interval and differentiable on the open interval.
f(5) = 2 and f(1) = 0 so the average rate of change is 1/2.
However, the instantaneous rate of change = 1/2 when x = 2, which is the x-value in that interval guaranteed by the MVT.
You can calculate this by finding f’(x), setting it = 1/2, and solving. f’(x) = 1 / √x-1