JEE Main 2023 · 12 April · morning · Single correct · +4 / −1
Given below are two statement: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: 5 f electrons can participate in bonding to a far greater extent than 4 f electrons
Reason R: 5 f orbitals are not as buried as 4 f orbitals
In the light of the above statements, choose the correct answer from the options given below
- (a) Both A and R are true and R is the correct explanation of A
- (b) Both A and R are true but R is NOT the correct explanation of A
- (c) A is true but R is false
- (d) A is false but R is true
Answer and solution
Answer (a) Both A and R are true and R is the correct explanation of A
Solution
Chemistry ma’am · 4 steps
Ask how deep each f subshell sits: 4f is tucked inside, 5f reaches out far enough to bond.
- Check R. In lanthanoids the 4f orbitals lie deep inside the atom, shielded by the filled 5s and 5p subshells. The 5f orbitals of actinoids extend further out and are less shielded, so they are not as buried. R is true.
- Check A. Because 5f electrons reach the outer region, they can overlap with ligand orbitals and take part in bonding. The deeply buried 4f electrons barely interact with ligands, so their part in bonding is very small. A is true.
- Link them. The greater bonding role of 5f electrons comes directly from their being less buried. This is also why actinoids show many oxidation states (up to +7), while lanthanoids stay mostly at +3. So R explains A.
- So. Both statements are true and R is the correct explanation of A, which is option (a).
The idea to keep. How deep an orbital is buried decides how much its electrons can bond. 4f is shielded by 5s² 5p⁶, 5f is more exposed, which is why actinoids show far more oxidation states than lanthanoids.
Answer from the NTA final answer key. Solution by PrepWiser.