<p>(a) Name the electromagnetic radiation that can be produced by a klystron or a magnetron valve. (1 Mark)</p>

<p>(b) Explain why the ozone layer, located at the top of the stratosphere, is crucial for human survival. (2 Marks)</p>

<p>(c) Arrange the following electromagnetic waves in descending order of wavelength:</p>

<p>Microwaves, Infrared rays, Ultraviolet radiation, &gamma;-rays. (2 Marks)</p>