Rusting of iron requires: MCQ with Answer and Explanation

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Rusting of iron requires:

A. Only water

B. Both oxygen and water

C. Carbon dioxide and water

D. Only oxygen

Answer: Option B

Solution (By JKSSB Mock Tests)

Rusting is an electrochemical process requiring both oxygen and water (moisture). The overall reaction: 4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃·xH₂O. In the absence of either, rusting does not occur. Salt accelerates rusting by increasing conductivity. Prevention methods include painting, greasing, galvanization, and cathodic protection. Rust is hydrated iron(III) oxide, a reddish-brown flaky substance, not protective.

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Question #1

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An indicator that remains colorless in acid and turns pink in base is:

A. Litmus

B. Turmeric

C. Phenolphthalein

D. Methyl orange

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Correct Answer: Option C

Explanation:
Phenolphthalein: pH range 8.3–10; colorless below 8.3, pink above. Litmus is red in acid, blue in base. Methyl orange red in acid, yellow in base. Turmeric yellow in acid, reddish-brown in base.

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Question #2

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Alpha rays are:

A. Electrons

B. Neutrons

C. Electromagnetic waves

D. Helium nuclei

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Correct Answer: Option D

Explanation:
Alpha rays consist of ⁴₂He²⁺ particles (2 protons + 2 neutrons). They have low penetration but high ionization power.

This question belongs to: Science chemistry

Question #3

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Assertion (A): Sodium chloride conducts electricity in its molten state. Reason (R): In the molten state, the ions are free to move and carry charge.

A. Both A and R are true and R is the correct explanation of A.

B. A is false but R is true.

C. Both A and R are true but R is NOT the correct explanation of A.

D. A is true but R is false.

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Correct Answer: Option A

Explanation:
Sodium chloride is an ionic compound. In the solid state, its Na+ and Cl- ions are held tightly in a crystal lattice and cannot move, so it doesn't conduct. When melted, the lattice breaks down, and the ions become mobile. These free-moving ions carry the electric current, making it a good conductor.

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