Question

Consider the following
Assertion (A): phosphorus can form both phosphorus (III) and phosphorus (V) chlorides but nitrogen cannot form nitrogen(V) chloride.
Reason (R): The electronegativity of nitrogen is more than that of phosphorus
The correct answer is

• A. Both (A) and (R) are correct, (R) is the correct explanation of (A)
• B. (A) is correct, but (R) is not correct
• C. Both (A) and (R) are correct, (R) is not the correct explanation of (A)
• D. (A) is not correct, but (R) is correct

Hint:

For questions about the valency of p-block elements, a key factor is the period number. Elements in the second period (like N, O, F) cannot expand their octet because they lack d-orbitals. Elements in the third period and below (like P, S, Cl) have vacant d-orbitals and can exhibit hypervalency (form more than four covalent bonds).

Answer 1

The Correct Option is C

Step 1: Analyze Assertion (A): Phosphorus (P) forms \( \text{PCl}_3 \) and \( \text{PCl}_5 \) because it has vacant d-orbitals in its valence shell, allowing it to expand its octet to hold 5 bonds. Nitrogen (N) forms \( \text{NCl}_3 \) but cannot form \( \text{NCl}_5 \) because it does not have vacant d-orbitals in its valence shell (n=2). It cannot expand its octet beyond 4 (maximum covalency is 4). So, Assertion (A) is Correct.
Step 2: Analyze Reason (R): The electronegativity of Nitrogen (3.0) is indeed higher than that of Phosphorus (2.1). So, Reason (R) is Correct.
Step 3: Establish the link: The inability of nitrogen to form pentahalides is due to the absence of d-orbitals, not because of electronegativity. While electronegativity is a true fact, it does not explain why \( \text{NCl}_5 \) doesn't exist. Therefore, R is not the correct explanation for A.