Correct Option (d):
The ionosphere is a region of the Earth's upper atmosphere, extending approximately from 60 km to 1000 km above the surface. It is characterized by a high concentration of free electrons and ions, which are formed primarily through the ionization of atmospheric gases by solar radiation.
Radio waves, particularly those in the shortwave and medium-frequency bands, are reflected or refracted by these free electrons back towards the Earth's surface. This phenomenon, known as skywave propagation, facilitates long-distance radio communication.
Statement 1 is incorrect. Ozone is predominantly found in the stratosphere (15-35 km altitude) and its primary function is to absorb harmful ultraviolet (UV) radiation from the Sun. Ozone does not play a role in the reflection of radio waves.
Statement 2 is incorrect. While radio waves do possess long wavelengths, their reflection by the ionosphere is not solely due to this characteristic. The reflection mechanism is fundamentally linked to the interaction of the radio waves with the free electrons present in the ionized layer, which alters the refractive index of the medium.
Incorrect Options:
Statement 1: The ionosphere's ability to reflect radio waves is not dependent on ozone. Ozone is primarily located in the stratosphere and absorbs ultraviolet radiation, not radio waves.
Statement 2: While radio waves are characterized by long wavelengths, this property alone does not explain their reflection by the ionosphere. The reflection mechanism is due to the interaction of radio waves with the free electrons in the ionized layer, causing refraction and eventual reflection.