Question

Given below are two statements :
Statement I : The correct order in terms of atomic/ionic radii is \( Al>Mg>Mg^{2+}>Al^{3+} \).
Statement II : The correct order in terms of the magnitude of electron gain enthalpy is \( Cl>Br>S>O \).
In the light of the above statements, choose the correct answer from the options given below :

• A. Both Statement I and Statement II are false
• B. Both Statement I and Statement II are true
• C. Statement I is false but Statement II is true
• D. Statement I is true but Statement II is false

Hint:

For isoelectronic ions, remember: Higher positive charge = smaller radius.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Atomic radius decreases across a period and increases down a group. Cations are always smaller than their parent atoms. Electron gain enthalpy becomes more negative (higher magnitude) towards the top right of the periodic table, with some anomalies.

Step 2: Detailed Explanation:
Statement I: In Period 3, Magnesium (\( Mg \)) is to the left of Aluminum (\( Al \)), so \( Mg \) has a larger atomic radius than \( Al \) (\( Mg>Al \)). Regarding ions, \( Mg^{2+} \) and \( Al^{3+} \) are isoelectronic. For isoelectronic species, the radius decreases with increasing nuclear charge. Thus, \( Mg^{2+}>Al^{3+} \).
The actual combined order is \( Mg>Al>Mg^{2+}>Al^{3+} \). Statement I is False.
Statement II: Halogens (\( Cl, Br \)) have much higher electron gain enthalpies than Group 16 elements (\( S, O \)). Between \( Cl \) and \( Br \), Chlorine is higher. Between \( S \) and \( O \), Sulfur has a higher magnitude than Oxygen due to interelectronic repulsions in the small Oxygen atom.
The order \( Cl>Br>S>O \) is correct in terms of magnitude. Statement II is True.

Step 3: Final Answer:
Statement I is false, and Statement II is true.