How many right angles do a semi circle have?

A semicircle itself does not have any right angles; it is a half-circle. However, if you consider the angle formed at the endpoints of the diameter when a line is drawn to any point on the arc of the semicircle, that angle is a right angle (90 degrees). Thus, while the semicircle itself has no right angles, it can form right angles with lines drawn to points on its arc.