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ICSE Class 9 Chemistry Question 6 of 39

Atomic Structure and Chemical Bonding — Question 12

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Question

Question 12

Identify the most stable atom from the following list. Give reason for your answer

23<em>11Na^{23}<em>{11}\text{Na},   35</em>17Cl^{35}</em>{17}\text{Cl},   40<em>18Ar^{40}<em>{18}\text{Ar},   27</em>13Al^{27}</em>{13}\text{Al}

Answer

The most stable atom from the given list is 1840Ar^{40}_{18}\text{Ar} (Argon).

Reason — Argon is a noble gas with a completely filled outermost shell, making it chemically inert and highly stable.
In contrast, the other atoms, 23<em>11Na^{23}<em>{11}\text{Na}, 35</em>17Cl^{35}</em>{17}\text{Cl}, 1327Al^{27}_{13}\text{Al}, have incomplete outer shells and are therefore reactive as they tend to gain, lose, or share electrons to achieve stability.