ANS:C - 3

There are 3 planes on which shear stress is 0 called principal planes. 1st is the major principle plane which has maximum compressive stress, 2nd minor principle plane on which compressive stress is minimum, and 3rd intermediate principle plane having compressive stress value between major and minor principal planes. There exist only two plane where there won't be any shear stress. They are major and minor principal stresses.

Refer to Mohr's Circle Diagram. The circle will coincide at two points on Normal Stress axis (X-Axis) , on which the Y-cord (Shear Stress) has to be equal to zero