In the code "7 C in the R", what familiar fact is this puzzle referring to?

Introduction / Context:
This question uses a well known style of abbreviation puzzle where a number and a series of letters stand for a familiar phrase. The code "7 C in the R" must be expanded into normal English words. In this case, the correct expansion is "7 colours in the rainbow". This refers to the traditional division of the visible spectrum into seven named colours: violet, indigo, blue, green, yellow, orange and red. Such puzzles help students connect symbolic representations with factual knowledge in a playful way.

Given Data / Assumptions:

• The pattern is "7 C in the R".
• The digit 7 probably refers to a count of items.
• The letter C likely stands for "colours" or another plural noun beginning with C.
• The letter R likely stands for a common noun starting with R, such as "rainbow".
• The target phrase should be a widely recognised fact.

Concept / Approach:
The basic method is to interpret each part of the code as the first letter of a word in a well known statement. Since the number 7 appears with the letter C, one natural guess is "7 colours". Next, we look at "R" and think of nouns related to colours that begin with R. The most famous is "rainbow". Together, "7 colours in the rainbow" is a standard phrase that describes a basic scientific and everyday observation about light dispersion. No other common fact with the same pattern is as well known or widely taught in schools.

Step-by-Step Solution:
Step 1: Treat "7 C" as "7 [something beginning with C]" and list possibilities such as colours, continents, candles, chords, or chapters. Step 2: Recognise that "in the R" should become "in the [something beginning with R]" such as rainbow, room, region, rulebook or refrain. Step 3: Combine plausible pairs and see which forms a standard fact, for example "7 colours in the rainbow". Step 4: Recall from basic science that the rainbow is traditionally described as having seven colours. Step 5: Confirm that "7 colours in the rainbow" matches both the code letters and a true, widely known fact.

Verification / Alternative check:
To verify, compare each answer choice. "7 continents in the region" is vague and not a fixed phrase; continents are global landmasses, not limited to a region. "7 candles in the room" and "7 chapters in the rulebook" describe arbitrary situations rather than universal facts. "7 chords in the refrain" is also not a standard musical rule. Only "7 colours in the rainbow" is both a common educational statement and a perfect match to the structure of the code. This confirms that it is the intended expansion.

Why Other Options Are Wrong:
7 continents in the region: Continents are not counted within "a region", and there are seven continents on Earth as a whole, not in one region.
7 candles in the room: Possible but arbitrary; not a universal statement that you would encode in a famous puzzle.
7 chapters in the rulebook: Different rulebooks have different numbers of chapters; seven is not a standard fixed number here.
7 chords in the refrain: Songs vary greatly and do not consistently use seven chords in a refrain.

Common Pitfalls:
Many learners may focus on the fact that there are seven continents and quickly choose an option that mentions continents, even if the rest of the phrase is unnatural. Others may forget that these abbreviation puzzles usually represent popular facts, proverbs, or standard lists taught in school. To avoid mistakes, always check that the reconstructed phrase is both grammatically smooth and well known. Remembering other examples like "7 D in a W" for "7 days in a week" can help you identify the intended style of knowledge.

Final Answer:
The code "7 C in the R" stands for the fact that there are 7 colours in the rainbow.