In our Solar System, which is considered the coldest of all the planets in terms of average atmospheric temperature?

Introduction / Context:
Planetary temperatures depend on distance from the Sun, atmosphere and internal heat. Questions about the hottest and coldest planets in the Solar System are very common in school level astronomy and general knowledge exams. This question asks which planet is considered the coldest when we look at average atmospheric temperature among the recognised planets.

Given Data / Assumptions:

• The question refers to planets of the Solar System, not dwarf planets.
• We compare outer gas and ice giants such as Uranus and Neptune.
• We assume a basic idea of planetary order from the Sun.

Concept / Approach:
Although Uranus and Neptune are both very cold and far from the Sun, studies show that Neptune tends to have slightly lower average atmospheric temperatures. Pluto used to be classified as a planet but is now considered a dwarf planet, so when the question uses the word planets, the comparison is among the eight major planets. By recalling this detail, you can identify Neptune as the coldest planet in terms of average atmosphere temperature.

Step-by-Step Solution:
Step 1: List outer planets that are very cold, mainly Uranus and Neptune. Step 2: Remember that both are ice giants but Neptune lies slightly farther from the Sun and has extremely low temperatures. Step 3: Note that Jupiter and Saturn are closer to the Sun and generally warmer than Uranus and Neptune. Step 4: Recognise that Pluto is now classified as a dwarf planet, not a main planet. Step 5: Conclude that Neptune is considered the coldest planet and select it as the answer.

Verification / Alternative check:
Astronomy sources show that the outer two planets Uranus and Neptune have very low average temperatures, but Neptune is usually described as slightly colder overall despite internal heat. Jupiter and Saturn, though having very cold upper atmospheres, are massive gas giants closer to the Sun. Pluto, while very cold, is now treated separately as a dwarf planet. When exam questions ask for the coldest planet, Neptune is the answer most aligned with current planetary classification, confirming option C as correct.

Why Other Options Are Wrong:
Jupiter is a gas giant with strong internal heating and is not the coldest planet.
Uranus is very cold but is slightly warmer on average than Neptune.
Pluto is a dwarf planet and no longer counted among the main planets in modern classification.
Saturn is also a gas giant with temperatures higher than those of Uranus and Neptune.

Common Pitfalls:
One common mistake is choosing Pluto because many older books treated it as the outermost planet and highlighted its low temperature. Another pitfall is confusion between Uranus and Neptune, which are both ice giants with similar properties. To avoid these issues, students should remember two points: Pluto is a dwarf planet under modern definitions, and Neptune is considered the coldest planet among the eight major planets.

Final Answer:
The coldest planet in our Solar System by average atmospheric temperature is Neptune.