Which of the following is the least dense planet in among all planets?

Appeared in: RML Lucknow - 2021

Explanation

Saturn is the least dense planet in our solar system, with an average density of approximately 0.687 g/cm³.
Its density is famously lower than that of water (1 g/cm³), meaning it would theoretically float in a sufficiently large body of water.
As a gas giant, Saturn is composed primarily of the light elements hydrogen and helium, which contributes to its low overall density despite its massive size.

Option A: Earth is a terrestrial (rocky) planet and is, in fact, the densest planet in the solar system with a density of 5.51 g/cm³.
Option B: Uranus, an ice giant, has a density of 1.27 g/cm³. While it is one of the four least dense planets, it is still significantly denser than Saturn.
Option C: Jupiter is the largest planet but not the least dense. Its immense gravity compresses its materials, giving it a density of 1.33 g/cm³, which is almost double that of Saturn.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Planetary Density as background academic context rather than a clinical decision trigger.
General knowledge questions are a common component of nursing entrance and recruitment exams to assess a candidate's overall awareness and reasoning skills.
A broad knowledge base can aid in building rapport with patients from diverse backgrounds and contributes to being a well-rounded professional.
What if the question asked for the 'largest' planet? The answer would change to Jupiter, highlighting the important distinction between size (volume) and density (mass per unit volume).

How to Approach the Question

First, identify the key concept in the question, which is 'least dense planet'.
Recall the basic classification of planets: rocky terrestrial planets (like Earth) and gas/ice giants (like Jupiter, Saturn, Uranus).
Remember the general principle that gas giants are much less dense than rocky planets. This immediately makes Earth the least likely answer.
Compare the remaining gas giants. Saturn is famously known for its extremely low density, a key characteristic often highlighted in basic astronomy.
Based on this specific fact, conclude that Saturn is the least dense planet among the options.

Concept Tested & Keywords

Concept Tested: Planetary Density
Stem keywords: least dense, planet
Lead-in keywords: least
Negative lead-in flag: LEAST changes the reasoning strategy; look for the exception or incorrect statement rather than the true statement.

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Practise the full RML Lucknow - 2021

Attempt every question from this paper in a timed mock, then review the full solution for each one.