The waves emitted when a metal target is bombarded with high energy electrons are

When a metal target is bombarded with high-energy electrons, the electrons decelerate rapidly upon hitting the target. This sudden deceleration of charged particles produces electromagnetic radiation.

The radiation produced in this process is called X-rays (specifically, Bremsstrahlung or braking radiation). This is the principle behind X-ray tubes, where high-energy electrons strike a metal target (like tungsten) to produce X-rays.

The correct answer is Option 3: X-rays.