Answer:
option D= Thermosphere
Step-by-step explanation:
Thermosphere:
It is the layer of earth which is present above the mesosphere and below the exosphere. In therosphere photoionization of molecules is occur due to U.V radiations and produce the ions in ionosphere.
Ionosphere:
It is present about 60 - 1,000 Km altitude of upper earth atmosphere and it is ionized part of atmosphere. It is present in thermosphere and parts of meso and exosphere. It is also called the extension of thermosphere. Although it is very small region but having great importance. Solar radiations ionized the ionosphere. It has many important role, for example in atmospheric electricity, creating the edge of magnetosphere and in radio communication to the long distance places of earth. The region present just below the ionosphere is termed as neutrosphere or neutral atmosphere.
Layers of ionization:
At the night significant ionization is occur in F layer but the ionization in D and E layer is not significant. In the day time too much heavy ionization is occur in D and E layer. The F layer create an other layer which called F1 and it is weaker ionization region. The ionization in F2 layer is occur day and night and this part is responsible for reflection and refraction of radio waves.