The correct answer is (d), the exosphere. The exosphere is the outermost layer of Earth’s atmosphere. It is very thin and extends from the top of the thermosphere to about 100,000 kilometers (62,000 miles) above Earth’s surface. The exosphere is so thin that there are very few molecules per cubic centimeter. The molecules in the exosphere are constantly escaping Earth’s gravity and being lost into space.
The troposphere is the lowest layer of Earth’s atmosphere. It extends from Earth’s surface to about 12 kilometers (7.5 miles) above sea level. The troposphere is where most of Earth’s weather occurs. The ozone layer is a region of Earth’s stratosphere that absorbs most of the Sun’s ultraviolet radiation. The ionosphere is a region of Earth’s atmosphere that is ionized by solar radiation. The ionosphere is important for radio communications.