A ray of light strikes a plane mirror XY at an angle of incidence of 65°, is reflected from this plane mirror and then strikes a second plane mirror YZ placed at right angles to the first mirror. What is the angle of reflection for the mirror YZ?

The mirrors XY and YZ are at right angles, i.e., perpendicular. When a ray of light strikes the XY mirror with 65degree angle, the incident angle will be 90-65= 25 degree on the YZ mirror. Since angle of incidence= angle of reflection, the angle of reflection for YZ mirror will be 25degrees.