Question

Given below are the two statements: one is labelled as Assertion (A) and the other is labeled as Reason (R).
Assertion (A): There is a considerable increase in covalent radius from N to P. However from As to Bi only a small increase in covalent radius is observed.
Reason (R): covalent and ionic radii in a particular oxidation state increases down the group.
In the light of the above statement, choose the most appropriate answer from the options given below:

• A. (A) is false but (R) is true
• 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. Both (A) and (R) are true and (R) is the correct explanation of (A)

Answer 1

The Correct Option is B

This problem requires assessing the connection between the provided assertion and reason, both concerning periodic trends in covalent radius down a group. To resolve this, we must analyze the underlying concepts.

1. Assertion Analysis:
   • Assertion (A): "Covalent radius increases significantly from N to P. However, from As to Bi, the increase in covalent radius is minimal."
   • Reason (R): "Covalent and ionic radii increase down a group for a given oxidation state."
2. Evaluation of Assertion (A):
   • Covalent radius typically expands down a group with the addition of new electron shells.
   • The N to P transition shows a substantial increase due to a new shell. From As to Bi, however, the presence of filled d and f orbitals reduces the effective nuclear charge, resulting in a less pronounced size increase. Therefore, Assertion (A) is accurate.
3. Evaluation of Reason (R):
   • The provided reason is correct. As one moves down a group, covalent and ionic radii generally enlarge due to the addition of electron shells.
4. Relationship Between Assertion (A) and Reason (R):
   • Although both statements are true, Reason (R) does not fully account for the minor increase from As to Bi, which is attributable to the poor shielding by f orbitals, a critical factor in this scenario.
5. Conclusion:
   • The most fitting selection is: "Both (A) and (R) are true, but (R) does not correctly explain (A)." This aligns precisely with the established facts and trends.

Consequently, the correct determination is that while both statements hold true, the reason insufficiently explains the assertion.