The loudness of the sound is measured in the unit known as:
The loudness of the sound is measured in the unit known as:
Options
Official answer
The correct option is D — Decibel.
Why this is correct:
- Decibel (dB) is the standard scientific unit used to measure the loudness/intensity of sound.
- It is the unit referred to in the NCERT discussion of noise pollution as an environmental problem.
Marking scheme
- 1.1 mark: correct identification of Decibel as the unit of loudness of sound.
Hint
Do not confuse 'Decibel' (a real unit of sound loudness) with 'Decimal' (a number system) — the two sound similar but are unrelated.
Quick oral answer
The loudness of sound is measured in decibels, the standard unit used to quantify noise pollution levels in environmental studies.
Common mistakes
- 1.Confusing 'Decibel' with the similarly-spelled but unrelated word 'Decimal' due to careless reading under exam time pressure.
- 2.Not recalling that noise pollution and its unit of measurement (decibel) is explicitly covered under environmental pollution in the Geography syllabus.
Analysis and explanation
Noise pollution is treated in NCERT as a form of environmental pollution caused by unwanted or excessive sound from traffic, industry, construction and other sources, and its intensity is quantified in decibels.
Why the distractors fail:
- Millimeter and Centimeter are units of length/distance, entirely unrelated to sound intensity.
- Decimal is not a unit of measurement at all — it refers to a number system/notation, making it a nonsensical option included as a distractor to test careful reading.
Why Decibel is correct:
- The decibel is a logarithmic unit used worldwide to express sound pressure level; the World Health Organisation and Indian pollution control norms both set permissible noise limits (e.g., 45 dB in residential areas at night) in decibels, which links directly to the environmental pollution content of the NCERT chapter.
Interesting facts
India's Central Pollution Control Board prescribes an ambient noise standard of 55 dB (day) and 45 dB (night) for residential areas.
The decibel scale is logarithmic, so a sound of 70 dB is ten times more intense than one of 60 dB, not just slightly louder.
Question details
Q14 of 36 questions
- Board
- CBSE
- Class
- Class 12
- Subject
- Geography
- Year
- 2026
- Section
- Section A
- Marks
- 1
- Type
- MCQ
- Chapter
- Geographical Perspective on Selected Issues and Problems (India: People and Economy)
- Topic
- Noise Pollution
- Bloom's level
- remember
- Syllabus topic
- Unit 4: Geographical Perspective on Selected Issues and Problems — Environmental Pollution: Noise Pollution and its Measurement
- Author
- CBSE
- Reviewed by
- Padhantu Academic Team
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Frequently asked questions
What is the permissible noise limit in Indian residential areas?
The Central Pollution Control Board prescribes ambient noise standards of 55 decibels during the day and 45 decibels at night for residential areas in India.
Why is 'Decimal' a plausible-looking wrong answer here?
'Decimal' sounds phonetically similar to 'Decibel' but refers to a number system/notation, not a unit of measurement, making it a deliberate distractor to test careful reading.