The concentration of dissolved oxygen in water is a measure of its: MCQ with Answer and Explanation

The concentration of dissolved oxygen in water is a measure of its:
A. Acidity
B. Hardness
C. Biological Oxygen Demand (BOD)
D. Purity
Answer: Option C
Solution (By JKExamLibrary)
The amount of dissolved oxygen is crucial for aquatic life. The Biological Oxygen Demand (BOD) is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material. High BOD indicates high organic pollution and low dissolved oxygen levels.

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Question #1
The relationship between volume and temperature for a fixed mass of gas at constant pressure was given by:
A. Charles
B. Gay-Lussac
C. Avogadro
D. Boyle

Correct Answer: Option A


Explanation:
Jacques Charles formulated the law: V ∝ T at constant P. Hence Charles' law. Gay-Lussac's law relates pressure and temperature at constant volume. Boyle's law: pressure-volume at constant temperature. Avogadro's law: volume-moles at same T & P. Charles also was a pioneer in ballooning.

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The main constituent of CNG is:
A. Propane
B. Ethane
C. Butane
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Correct Answer: Option D


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CNG (Compressed Natural Gas) is primarily methane (CH₄). LPG is propane and butane. Methane is the lightest hydrocarbon. CNG is a cleaner fuel for vehicles.

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Question #3
The force that holds atoms together in a molecule is called:
A. Nuclear force
B. Chemical bond
C. Gravitational force
D. Magnetic force

Correct Answer: Option B


Explanation:
Chemical bonds are attractive forces between atoms due to electron interaction—ionic (transfer), covalent (sharing), metallic, etc. These bonds hold atoms together in molecules or crystals. Nuclear force holds protons and neutrons in nucleus. Gravitational and magnetic forces are negligible at atomic scale. Bond energy determines stability; stronger bond means more energy required to break.

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