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NEET Chemistry QUESTION #7398

Question 1

The correct order of sizes for the following species is:

\(\text{Ca}^{2+} < \text{K}^+ < \text{Ar} < \text{Cl}^- < \text{S}^{2-}\)
\(\text{Ar} < \text{Ca}^{2+} < \text{K}^+ < \text{Cl}^- < \text{S}^{2-}\)
\(\text{Ca}^{2+} < \text{Ar} < \text{K}^+ < \text{Cl}^- < \text{S}^{2-}\)✔️
\(\text{Ca}^{2+} < \text{K}^+ < \text{Ar} < \text{S}^{2-} < \text{Cl}^-\)

Correct Answer Explanation

All species are isoelectronic (18 electrons).
Size decreases as nuclear charge increases (more protons pull same electrons closer):

\(\text{Ca}^{2+}\): Z=20
\(\text{Ar}\): Z=18
\(\text{K}^+\): Z=19
\(\text{Cl}^-\): Z=17
\(\text{S}^{2-}\): Z=16

Increasing size: \(\text{Ca}^{2+} < \text{K}^+ < \text{Ar} < \text{Cl}^- < \text{S}^{2-}\)