Question

The thickness of a CD ROM Is..........mm approximately.

• A. 1.22
• B. 1.5
• C. 0.66
• D. None of these

Hint:

The physical base dimensions of standard optical discs (CDs, DVDs, Blu-rays) are universally identical to ensure backward compatibility across different optical disk drives: 120 mm in overall diameter and 1.2 mm in thickness.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks for the standard or approximate physical thickness of a CD ROM in millimeters.


Step 2: Detailed Explanation:
According to the foundational physical specifications (the Red Book standard) for optical discs like CDs, the physical dimensions are strictly predefined for global manufacturing consistency.
A standard CD is exactly 120 mm in diameter and exactly 1.2 mm in thickness.
Looking at the provided options, 1.22 mm is very close to 1.2 mm but is technically inaccurate for a strict standard.
Since 1.2 mm is the precise industry standard and none of the numerical options (1.22, 1.5, 0.66) completely match this established value, the most accurate multiple-choice selection is "None of these".


Step 3: Final Answer:
The exact standard thickness of a CD ROM is 1.2 mm. Therefore, none of the given exact numeric options are completely correct.

Answer 2

This question asks for the approximate thickness, in millimetres, of a standard CD-ROM. Rather than starting from the manufacturing standard, let's test the plausibility of each numeric option against what is physically known about optical discs.

1. 1.22: This value is extremely close to the well known industry figure of 1.2 mm, which makes it tempting, but it is not the exact standardized measurement. A specification this precise would be quoted exactly rather than rounded to a slightly different decimal, so this value does not represent the true thickness.
2. 1.5: A disc this thick would be noticeably bulkier than a standard CD and closer to some non-standard specialty media. Given how thin an actual CD feels, 1.5 mm overstates the real thickness.
3. 0.66: This is roughly half of the true thickness. A disc this thin would be extremely flexible and fragile, more comparable to a single internal layer than the complete assembled disc, so it understates the real value.
4. None of these: Since the actual accepted thickness of a standard CD is 1.2 mm exactly, and none of the three numeric options state 1.2 precisely, this option correctly captures that no listed figure matches.

Testing each number against the physical scale of a real disc shows that the first three options are all either slightly off or way off the mark, while the true figure of 1.2 mm simply isn't listed.

Therefore, the correct answer is None of these.