Final answer:
The atmospheres of the gas and ice giants are rich in hydrogen and helium due to their massive a) gravitational capture of hydrogen and helium during the solar system's formation. Jupiter and Saturn, being larger, captured more and have atmospheres closer in composition to the Sun. Uranus and Neptune, less massive, have higher proportions of icy and rocky materials.
Step-by-step explanation:
The atmospheres of Jupiter, Saturn, Uranus, and Neptune contain large amounts of hydrogen and helium primarily due to gravitational capture of hydrogen and helium during the early stages of the solar system's formation. Each of these giant planets, often referred to as gas giants for Jupiter and Saturn, and ice giants for Uranus and Neptune, initially formed from a core of ice and rock. They captured the lighter gases efficiently due to their massive gravitational fields, leading to atmospheres rich in hydrogen, the primary component of their composition.
The collapse of gas from the solar nebula onto these cores is why the gas giants acquired a hydrogen-rich composition similar to the Sun. Jupiter and Saturn, being more massive, captured more of these gases, whereas Uranus and Neptune have compositions more dominated by icy and rocky materials due to capturing much less gas. Additionally, the reducing environment of the outer solar system led to the formation of hydrogen-based gases such as methane (CH₄) and ammonia (NH₃) in these atmospheres.
Hence, the correct answer is Option A.