In basic astronomy and general science, which planet in our solar system is popularly known as the red planet because of its reddish appearance when viewed from Earth?

Introduction / Context:
Planets often have popular nicknames based on their appearance or other distinctive characteristics. One of the most famous is the red planet, a term frequently used in schoolbooks, science magazines and media reports. This question asks you to recall which planet in our solar system is commonly referred to by this nickname and to distinguish it from other planets that may also appear bright or coloured in the night sky.

Given Data / Assumptions:

• The nickname red planet refers to the overall reddish colour of the planet as seen from Earth.
• Mars has a surface rich in iron oxides, giving it a reddish appearance.
• Mercury and Venus are bright but do not appear distinctly red; Pluto is a distant dwarf planet and is not typically associated with this nickname.
• The question is concerned with common general knowledge usage rather than detailed spectral data.

Concept / Approach:
Mars is widely known as the red planet because its surface contains iron rich minerals that have oxidised, giving it a rusty reddish colour. This hue makes Mars stand out in the night sky as a reddish point of light. Mercury appears more greyish and is often difficult to see, Venus appears as a bright white or yellowish evening or morning star, and Pluto is too faint to be seen without telescopes and is usually classified as a dwarf planet. Because of its distinct colour and widespread cultural recognition, Mars is the only planet commonly called the red planet in both scientific and popular contexts.

Step-by-Step Solution:
Step 1: Recall that Mars has a reddish surface due to iron oxide rich dust and rocks, which is why it is popularly called the red planet. Step 2: Consider the appearance of Mercury, which is small and greyish, not strongly red when viewed from Earth. Step 3: Note that Venus is very bright but appears more white or yellowish than red. Step 4: Recognise that Pluto is a distant dwarf planet and is not commonly associated with the nickname red planet in school level general knowledge. Step 5: Select Mars as the planet widely and consistently known as the red planet.

Verification / Alternative check:
Science textbooks, documentaries and space agency materials refer to Mars as the red planet because of its colour and the dusty iron rich surface. Space missions such as orbiters and rovers sent to Mars are often described as exploring the red planet. Planetary identification charts and classroom posters also label Mars with this nickname. No similar widespread nickname associates Mercury, Venus or Pluto with the phrase red planet, confirming that Mars is the intended and correct answer in this question.

Why Other Options Are Wrong:
Option a, Mercury, is close to the Sun and appears as a small greyish or slightly yellowish point, not distinctly red, and is not known as the red planet.

Option b, Pluto, is now classified as a dwarf planet and is not visible to the unaided eye, nor commonly nicknamed the red planet.

Option d, Venus, is often called the morning star or evening star due to its brightness and white or yellowish appearance, not for any red colour.

Common Pitfalls:
Learners might confuse Mars with Venus because both are visible and sometimes bright, but only Mars appears strongly reddish. Others may be influenced by images of distant trans Neptunian objects with varied colours and mistakenly think of Pluto or other bodies. Anchoring the nickname red planet firmly to Mars and remembering its rusty surface from rover photographs helps to avoid such confusion in exams and quizzes.

Final Answer:
The planet known as the red planet is Mars.