Steps to construct 90° angle with compass and ruler are provided.
Construction of 90º Angle
Draw a line AB
Draw an arc with A as a centre which cuts AB at point C.
Draw another arc with same radius at c that cuts arc at point D.
Draw an arc with D as a centre taking same radius which cuts arc at E.
Draw an arc taking radius more than half of the arc DE from point D and E.
Mark the point of intersection as F. Join F to A. ∠FAB = 900