(a)
Hint: Ionosphere reflects only short-wave bands.
Step: Identify the condition for reflection.
Long-distance radio broadcasts use shortwave bands because the ionosphere can only reflect these bands.

(b)
Hint: Satellites are helpful in reflecting TV signals.
Step: Identify the condition for reflection.
Television signals are of high frequencies and high energies and are not reflected by the ionosphere. Hence, satellites are helpful in reflecting TV signals. Also, they help in long-distance TV transmissions.

(c)
Hint: Visible and radio waves can penetrate the atmosphere.
Step: Identify the waves with high energies.
With reference to X-ray astronomy, X-rays are absorbed by the atmosphere. However, visible and radio waves can
penetrate it. Hence, optical and radio telescopes are built on the ground, while X-ray astronomy is possible only with the
help of satellites orbiting the Earth.

(d)
Hint: Ozone layer protects from harmful ultraviolet radiation.
Step: Identify the harmful radiations received from the earth.
The small ozone layer on the tap of the atmosphere is crucial for human survival
because it absorbs harmful ultraviolet radiations present in sunlight and prevents it from reaching the Earth's surface.

(e)
Hint: Recall greenhouse effect.
Step:  Find the effect of the atmosphere.
In the absence of an atmosphere, there would be no greenhouse effect on the surface of the Earth. As a result, the temperature of the Earth would decrease rapidly, making it chilly and difficult for human survival.

(f)
Hint: Temperature falls after a post-nuclear war.
Step: Find the consequence of post-nuclear war.
A global nuclear war on the surface of the Earth would have disastrous consequences.
Post-nuclear war, the Earth will experience severe winter as the war will produce clouds of smoke that would cover maximum parts of the sky, thereby preventing solar light from reaching the atmosphere. Also, it will lead to the depletion of the ozone layer.