Q.115 Botany ⭐ 360° Option Elimination Active

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NEET 2023 Botany Question 115 Solution

Topic: Environmental Issues · Official NTA Booklet Code G5

Question

The thickness of ozone in a column of air in the atmosphere is measured in terms of:

(1)Kilobase
(2)Dobson units
(3)Decibels
(4)Decameter

✓

Verified Against NTA Final Answer Key

Option (2) : Dobson units

📚 Environmental Issues Easy

📋 Given Parameters & Problem Setup

Parameter Thickness of stratospheric ozone column

Standard Unit Dobson Units (

DU

)

⚡

The 30-Second Exam Hall Shortcut: ⚡ Atmospheric Unit Anchor: Ozone Column = Dobson Units (DU)

⏱️ Save ~25 seconds

The standard physical unit to quantify the thickness of ozone in a vertical column of air from the ground to the top of the atmosphere is Dobson Units (DU). $1\text{ DU} = 0.01\text{ mm}$ pure ozone at STP!

1 Kilobase (

kb

): Unit of nucleic acid length (1000 base pairs).

2 Decibel (

dB

): Unit of sound intensity / acoustic loudness.

3 Decameter (

dam

): Metric unit of distance (10 meters).

4 Dobson Unit (

DU

): Unit of ozone column thickness.

5 Match Option (2) Dobson units.

🛡️

Why You Can 100% Trust This Shortcut: Canonical NCERT Environmental Issues stratospheric physics measurement standards.

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Definition of Dobson Unit (DU)

One Dobson Unit ( $1\text{ DU}$ ) is defined as the thickness of a pure layer of ozone that would be formed if the entire atmospheric ozone column were compressed to Standard Temperature and Pressure ( $STP: 0^\circ\text{C}, 1\text{ atm}$ ):

1\text{ DU} = 10\,\mu\text{m} = 0.01\text{ mm of pure } O_3 \text{ at STP} \quad (\approx 2.69 \times 10^{16} \text{ molecules/cm}^2)

Step 2

Verbatim NCERT Statement

NCERT states verbatim: "The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units (DU)."

Step 3

Evaluation of Distractor Units

Kilobase is a genetic measurement ( $10^3\text{ bp}$ of DNA). Decibel ( $dB$ ) measures acoustic sound pressure level ( $>150\text{ dB}$ damages eardrums). Decameter is an SI distance unit ( $10\text{ m}$ ).

⭐

360° Option Elimination Engine Key Feature

Diagnose every choice: Know exactly why the right option works and why distractors fail.

4-Option Deep Scan

1 1

✗ Incorrect

Verdict & Scientific Reason:

Kilobase ( $kb$ ) measures DNA/RNA sequence length, not atmospheric gas concentration.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing molecular biology terminology with atmospheric chemistry.

2 2

✓ 100% Correct

Verdict & Scientific Reason:

Standard international and NCERT unit for atmospheric ozone column thickness ( $DU$ ).

💡

Why this is airtight: None; textbook verbatim.

3 3

✗ Incorrect

Verdict & Scientific Reason:

Decibel ( $dB$ ) is the logarithmic unit of acoustic loudness and noise pollution.

⚠️

Student Fallacy (Why candidates pick this trap): Conflating noise pollution units with atmospheric ozone layers.

4 4

✗ Incorrect

Verdict & Scientific Reason:

Decameter is a linear distance unit ( $10\text{ meters}$ ), inapplicable to gas column density.

⚠️

Student Fallacy (Why candidates pick this trap): Guessing a metric distance prefix.

⚠️

NTA Trap Alert: Acoustic vs. Ozone Unit Confusion

Both Decibels ( $dB$ ) and Dobson units ( $DU$ ) begin with "D", leading inattentive students under exam pressure to misread the choices.

🛡️ How to avoid the -1 mark: Decibels (

dB

) = Sound/Noise. Dobson Units (

DU

) = Ozone column thickness.

📖

Core NEET Syllabus Standard

NCERT Biology · Environmental Issues Standard Benchmark

Core Scientific Principle Tested:

"The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units (DU)."

Syllabus Focus: Ozone Depletion in the Stratosphere

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2023 Botany Question 115 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Atmospheric Unit Anchor: Ozone Column = Dobson Units (DU)

Step-by-Step Rigorous Workflow & Mathematical Proof

Definition of Dobson Unit (DU)

Verbatim NCERT Statement

Evaluation of Distractor Units

360° Option Elimination Engine Key Feature

NTA Trap Alert: Acoustic vs. Ozone Unit Confusion

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Environmental Issues

Measurement of Stratospheric Ozone Layer Thickness (Dobson Units)

Montreal Protocol (1987): Control of Ozone Depleting Substances

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