Alicia is listening to a song on the radio. which atmospheric layer allows her to hear the song?

ionosphere
troposphere
mesosphere
stratosphere

The ionosphere allows Alicia to her the song on radio.

Explanation:

The ionosphere is in the upper atmosphere. It affects the propagation of radio waves because is where sufficient ionization can exist. The radiation from the sun in this layer ionizes atoms and molecules here, the molecules liberate electrons and they create a space of free electron and ions.

Radio waves are affected by the ionosphere because radio waves in this frequency range are effectively reflected by the ionosphere, they don´t penetrate through the atmosphere. This reflections enable wave propagation large distance.

The ionosphere affects the radio spectrum from low frequencies up to super high frequencies.  

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