Assertion (A): The noble gases are placed in Group 18. Reason (R): They have a completely filled outermost shell (except Helium) and zero valency. MCQ with Answer and Explanation

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Assertion (A): The noble gases are placed in Group 18. Reason (R): They have a completely filled outermost shell (except Helium) and zero valency.

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

Answer: Option A

Solution (By JKSSB Mock Tests)

Noble gases have completely filled valence shells (ns²np⁶, except He which is 1s²), making them highly stable and unreactive with a valency of zero. Because of this unique stability and distinct electronic configuration, they form a separate group, Group 18, in the modern periodic table.

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Question #1

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Which of the following is a chemical property of a substance?

A. Melting point

B. Boiling point

C. Reactivity with acid

D. Density

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Correct Answer: Option C

Explanation:
Chemical properties describe a substance's ability to undergo chemical changes—reactivity with acid, flammability, oxidation states, etc. Melting point, density, boiling point are physical properties that can be observed without changing composition. Reactivity with acid involves formation of new substances. A piece of magnesium reacting with HCl is a chemical change.

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Question #2

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Which radiation is the most penetrating?

A. Gamma

B. Beta

C. Positron

D. Alpha

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Correct Answer: Option A

Explanation:
Gamma rays are electromagnetic waves with no mass and no charge, thus they interact least with matter and have the highest penetrating power. Alpha particles (He nuclei) are stopped by paper. Beta particles (electrons) can be stopped by aluminum. Gamma requires thick lead or concrete.

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Question #3

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The process of converting one element into another by bombarding it with high-energy particles is called:

A. Nuclear fusion

B. Radioactive decay

C. Nuclear fission

D. Artificial transmutation

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Correct Answer: Option D

Explanation:
Artificial transmutation is the conversion of a chemical element or an isotope into another through a nuclear reaction induced by bombarding it with high-energy particles (like alpha particles, protons, or neutrons). This was first achieved by Rutherford in 1919 when he converted nitrogen into oxygen.

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