Number of elements from the following that CANNOT form compounds with valencies which match with their respective group valencies is . B, C, N, S, O, F, P, Al, Si
- 7
- 3
- 5
- 6
Answer
(2) 3
Solution
Group valency (p-block) = number of valence electrons
∵ 2nd-period elements have no d orbitals ⇒ maximum covalency 4
B, Al (3): BCl3, AlCl3 ✓; C, Si (4): CCl4, SiCl4 ✓
P (5): PCl5 ✓; S (6): SF6 ✓
N (5): no NCl5 ✗; O (6): no OF6 ✗; F (7): no FCl7 ✗
∴ N, O, F ⇒ 3
Answer: (2)