Question

Given below are two statements: Statement-I: The correct order for radius is \[ \mathrm{Al > Mg> Mg^{2+} > Al^{3+}} \] Statement-II: Atomic size always depends on electronegativity. In the light of the above statements, choose the correct option.

• A. Statement-I and Statement-II are correct
• B. Both Statement-I and Statement-II are incorrect
• C. Statement-I is correct but Statement-II is incorrect
• D. Statement-I is incorrect but Statement-II is correct

Answer 1

The Correct Option is B

Concept: Atomic and ionic radii depend on several factors such as:

• Nuclear charge
• Number of shells
• Shielding effect
• Charge on the ion

Electronegativity is not the sole deciding factor for atomic size.

Analysis of Statement-I:

Consider neutral atoms \( \text{Mg} \) and \( \text{Al} \):

• \( \text{Mg} \) and \( \text{Al} \) lie in the same period (Period 3).
• Across a period, atomic radius decreases due to increasing nuclear charge.

Hence, the given order \( \text{Al} > \text{Mg} \) is incorrect because of the trend of atomic radius across a period.

Now consider the ions:

• Cations are smaller than their parent atoms, so \( \text{Mg}^{2+} > \text{Al}^{3+} \).
• Higher the positive charge, smaller the ionic radius.

The correct ionic order should be:

\[ \text{Mg} > \text{Al} > \text{Mg}^{2+} > \text{Al}^{3+} \]

Thus, the overall order should be \( \text{Mg} > \text{Al} > \text{Mg}^{2+} > \text{Al}^{3+} \), and Statement-I is incorrect.

Analysis of Statement-II:

The statement says: \( \text{Mg}^{2+} > \text{Al}^{3+} \) and \( \text{Mg} > \text{Al} > \text{Mg}^{2+} > \text{Al}^{3+} \)

However, the statement is incorrect because:

• Atomic size primarily depends on nuclear charge and shielding effect.
• Electronegativity is a consequence of atomic size, not the controlling factor.
• The word "always" makes the statement absolutely false.

Thus, Statement-II is also incorrect.

Final Conclusion:

Both Statement-I and Statement-II are incorrect.