Which of the following is NOT a method of water purification? MCQ with Answer and Explanation

Which of the following is NOT a method of water purification?
A. Boiling
B. Chlorination
C. Filtration
D. Electrolysis
Answer: Option D
Solution (By JKExamLibrary)
Electrolysis of water decomposes it into hydrogen and oxygen, not purification. Boiling kills microbes, filtration removes particulate matter, chlorination disinfects. Other methods: UV treatment, ozonation, reverse osmosis, distillation. Electrolysis is a chemical decomposition technique.

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Question #1
Vulcanized rubber has better properties due to:
A. Addition of carbon black
B. Removal of impurities
C. Cross-linking of polymer chains with sulfur
D. Addition of plasticizers

Correct Answer: Option C


Explanation:
Sulfur forms disulfide cross-links between polyisoprene chains, providing elasticity, tensile strength, and resistance to temperature changes. Carbon black is filler/additive for reinforcement but not the vulcanization agent.

This question belongs to: Science chemistry
Question #2
Which allotrope of carbon is the hardest natural substance?
A. Lamp black
B. Coal
C. Diamond
D. Graphite

Correct Answer: Option C


Explanation:
Diamond is the hardest known natural material due to its rigid three-dimensional network of covalent bonds with sp³ hybridization, forming a tetrahedral structure. Graphite is soft and slippery because of its layered structure with weak van der Waals forces between layers. Coal is an amorphous form of carbon. Diamond is used in cutting, drilling, and jewelry. Mohs hardness of diamond is 10.

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Question #3
Which of the following compounds contains a coordinate covalent bond?
A. NaCl
B. NH₄⁺
C. Cl₂
D. H₂O

Correct Answer: Option B


Explanation:
In the ammonium ion (NH₄⁺), the nitrogen atom in ammonia (NH₃) shares its lone pair of electrons with a hydrogen ion (H⁺) which has no electrons. This type of bond, where both shared electrons are donated by a single atom, is a coordinate covalent (dative) bond.

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