Question

Consider the following two statements: 
Statement I: Among Mg, Al, Mg\(^2\), Al\(^3\), the one having smallest size is Al\(^3\) 
Statement II: Eu is having exceptionally high atomic radii among lanthanide elements The correct answer is:

• A. Both statements I and II are correct
• B. Both statements I and II are not correct
• C. Statement I is correct but statement II not correct
• D. Statement I is not correct but statement II is correct

Hint:

When comparing ions of the same period, the ionic size decreases as the positive charge on the ion increases.

Answer 1

The Correct Option is A

Statement I: The ionic size of Al\(^3\) is the smallest among the given ions (Mg\(^2\), Al\(^3\), Mg\), since the size decreases as the charge increases for the same period.
Statement II: Eu (Europium) has one of the largest ionic radii among the lanthanides, and this is a known fact in periodic trends.
Thus, both statements I and II are correct.

Answer 2

Step 1: Analyze Statement I – Comparison of atomic and ionic sizes.
Given species: Mg, Al, Mg\(^{2+}\), Al\(^{3+}\)
- Mg and Al are neutral atoms. Al has a smaller size than Mg due to increased nuclear charge across the period.
- Mg\(^{2+}\) and Al\(^{3+}\) are cations. When atoms lose electrons, they become smaller due to reduced electron-electron repulsion and increased effective nuclear charge.
- Al\(^{3+}\) has the highest positive charge and smallest number of electrons, leading to the strongest effective nuclear pull on electrons.
Therefore, Al\(^{3+}\) has the smallest size among the given species.
✔️ Statement I is correct.

Step 2: Analyze Statement II – Exceptional atomic radius of Europium (Eu).
- In the lanthanide series, atomic radii generally decrease with increasing atomic number, a phenomenon known as lanthanide contraction.
- Europium (Eu), however, shows an anomaly due to its half-filled 4f⁷ configuration, which is relatively stable.
- This leads to reduced nuclear attraction and hence a slightly larger radius than expected.
So, Eu does have an exceptionally high atomic radius among lanthanides.
✔️ Statement II is also correct.

Step 3: Conclusion.
✅ Both statements I and II are correct.
Hence, the correct answer is: Both statements I and II are correct.