MCQ Detailed View

The planets Uranus and Neptune, known as ice giants, are composed mainly of volatile substances, which are chemical compounds that can easily change between solid, liquid, and gas states under certain conditions. These volatiles are mostly water (H₂O), ammonia (NH₃), and methane (CH₄). Together, they make up a large portion of the planets’ interiors, surrounding their rocky cores.

Unlike the gas giants Jupiter and Saturn, which consist mostly of hydrogen and helium gases, ice giants formed farther away from the Sun in colder regions of the Solar System. At such low temperatures, water, ammonia, and methane condensed into icy forms during planetary formation billions of years ago. This is why these substances dominate the composition of Uranus and Neptune, giving them their name as "ice giants."

Water ice is the most abundant, forming thick layers deep inside these planets. Ammonia ice combines with water under high pressure, contributing to their unique internal chemistry. Methane is present both in the atmosphere and deeper layers, playing a significant role in the planets’ blue coloration. Methane absorbs red wavelengths of sunlight and reflects blue light, making Uranus and Neptune appear blue when observed from space.

Mercury and plasma are not major components of these planets, which is why other answer choices are incorrect. Mercury is a heavy element found in trace amounts only, while plasma is not a primary constituent of their structure.

Key facts:

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  Main volatiles: Water, ammonia, and methane

  
  


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  Location: Outer Solar System, beyond Saturn

  
  


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  Effect on appearance: Methane causes blue coloration

  
  


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  Difference from gas giants: Higher proportion of ices than hydrogen and helium

  
  

Thus, the correct answer is Water, ammonia, and methane, which make up most of the volatile substances inside ice giants.