Question

Which of the following sets are correctly matched?

• A. I, II, III
• B. I, II Only
• C. II, III Only
• D. I, III Only

Hint:

{IE Exceptions to remember:} Group 2 ($ns^2$) elements have higher IE than Group 13 ($np^1$) elements (e.g., $Be>B, Mg>Al$). Group 15 ($np^3$) elements have higher IE than Group 16 ($np^4$) elements (e.g., $N>O, P>S$).

Answer 1

The Correct Option is A

Step 1: Check Set I (Atomic Radius):
Trend: Atomic radius decreases from left to right across a period due to increasing effective nuclear charge. Elements: Li ($Z=3$), Be ($Z=4$), B ($Z=5$), C ($Z=6$). Correct Order: $Li>Be>B>C$ (or $C<B<Be<Li$). Status: Correct.
Step 2: Check Set II (Ionization Enthalpy - IE):
Trend: Generally increases left to right. Exceptions:

• Be ($2s^2$)>B ($2p^1$) (Penetration/Stability).
• Mg ($3s^2$)>Al ($3p^1$) (Stability of full s-orbital).

Elements: Na ($Z=11$), Mg ($Z=12$), Al ($Z=13$), Si ($Z=14$). Correct Order: $Na<Al<Mg<Si$. (Al comes before Mg due to the exception). Status: Correct.
Step 3: Check Set III (Electronegativity):
Trend: Increases left to right across a period. Elements from Group 13 to 15: Al (1.61), Si (1.90), C (2.55), N (3.04). Although Al and Si are period 3 and C and N are period 2, N is the most electronegative, followed by C. Metals/Metalloids (Al, Si) have lower EN. Correct Order: $Al<Si<C<N$. Status: Correct.
Step 4: Conclusion:
All three sets are correctly matched.