Answer B.
We can find the lengths of the sides of the triangle by finding the difference in the coords of two points, and then using Pythagoras to find the length of the side joining the two points. When we do this we get XZ and YZ = √5 and XY = √10, the hypotenuse, since XZ²+YZ²=XY², so the right angle, being opposite the hypotenuse, is angle Z.