The correct answer is A. Troposphere.
The troposphere is the lowest layer of Earth’s atmosphere. It extends from the surface of the Earth to an average height of about 12 kilometers
(7.5 miles). The troposphere is where most of Earth’s weather occurs. The temperature in the troposphere decreases with increasing altitude. This is because the air in the troposphere is heated by the Earth’s surface. The Earth’s surface absorbs energy from the sun and re-emits that energy as heat. The air in the troposphere is heated by this heat, and the warmer air rises. As the air rises, it cools and becomes denser. The denser air sinks back down to the surface, where it is heated again. This cycle of rising and sinking air creates the winds and other weather patterns that we see in the troposphere.The stratosphere is the next layer of Earth’s atmosphere, above the troposphere. It extends from an average height of about 12 kilometers (7.5 miles) to an average height of about 50 kilometers (31 miles). The stratosphere is much colder than the troposphere. The temperature in the stratosphere increases with increasing altitude. This is because the ozone layer, which absorbs ultraviolet radiation from the sun, is located in the stratosphere. The ozone layer heats the stratosphere by absorbing this radiation.
The mesosphere is the next layer of Earth’s atmosphere, above the stratosphere. It extends from an average height of about 50 kilometers (31 miles) to an average height of about 85 kilometers (53 miles). The mesosphere is the coldest layer of Earth’s atmosphere. The temperature in the mesosphere decreases with increasing altitude. This is because there is very little air in the mesosphere. The air in the mesosphere is so thin that it does not absorb much heat from the sun.
The ionosphere is the outermost layer of Earth’s atmosphere. It extends from an average height of about 85 kilometers (53 miles) to an average height of about 600 kilometers (373 miles). The ionosphere is named for the fact that it is ionized, meaning that it contains a large number of charged particles. The charged particles in the ionosphere are created by the sun’s ultraviolet radiation. The ionosphere is important for radio communications because it reflects radio waves back to Earth.