The zero of the graduated circle of a prismatic compass is located at

ANS:C - south end

This is one of the special cases in prismatic compass just imagine the needle is pointing magnetic north and you look reading through a prism south being the closest direction hence you actually read a vertically opposite angle so this is the reason you have zero at the south. As per my knowledge; 0 at South, 90 at the West, 180 at the North and 270 at the East. And in the surveyor compass, 0 at North and South, 90 at East and West.