Concept: The question tests on basics of of Coordinate Geometry
Solution:
If we take point C as (1, 1), we get a right angled triangle with base length = 5 - 1 = 4
and height = 4 - 1 = 3
By the Pythagoras theorem
AC = Length of the hypotenuse = √4^2+3^2=16+9
=√25
=5
Alternately, you can use the distance formula between 2 points
= √(y1−y2)^2+(x1−x2)^2
=√4−1)^2+(1−5)^2
=3^2+4^2
√9+16
=√25=5
Option B