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. MCQ with Answer and Explanation

Question

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 but R is NOT the correct explanation of A.

B. A is true but R is false.

C. A is false but R is true.

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

Answer: Option D

Solution (By JKExamLibrary)

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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Question #1

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The element with atomic number 20 has the electronic configuration:

A. 2,8,8,4

B. 2,8,18,2

C. 2,8,8,2

D. 2,8,10

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Correct Answer: Option C

Explanation:
Atomic number 20 is calcium (Ca). Electron shells fill according to 2n²: K=2, L=8, M can hold 18 but fourth shell (N) starts after 8 electrons in M due to energy level considerations (Aufbau principle). So Ca configuration is 2,8,8,2. It has 2 valence electrons, belongs to Group 2, Period 4. Its nearest noble gas is Ar (2,8,8).

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Question #2

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Which of the following is an example of a synthetic detergent?

A. Calcium oleate

B. Sodium stearate

C. Potassium palmitate

D. Sodium lauryl sulfate

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Correct Answer: Option D

Explanation:
Sodium lauryl sulfate (CH₃(CH₂)₁₁OSO₃Na) is a synthetic detergent with a sulfate group. Sodium stearate and potassium palmitate are soaps (carboxylate salts). Calcium oleate is soap scum.

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Question #3

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Which of the following oxides is amphoteric?

A. SO₂

B. MgO

C. Al₂O₃

D. Na₂O

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Correct Answer: Option C

Explanation:
Amphoteric oxides react with both acids and bases to form salts and water. Aluminum oxide (Al₂O₃) and Zinc oxide (ZnO) are classic examples. Na₂O and MgO are basic oxides that react only with acids, while SO₂ is an acidic oxide that reacts only with bases.

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