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

The question involves evaluating the relationship between the assertion and reason provided, both of which pertain to periodic trends in the covalent radius of elements down a group in the periodic table. To answer this, we need to examine the concepts involved.

1. Understanding the Assertions:
   • 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 specific oxidation state increase down the group."
2. Evaluating Assertion (A):
   • The covalent radius generally increases as we move down a group, due to additional electron shells being added, increasing the size of the atom.
   • From Nitrogen (N) to Phosphorus (P), a considerable increase is seen because of the addition of a new shell. However, from Arsenic (As) to Bismuth (Bi), filled d and f orbitals come into play, causing less effective nuclear charge which leads to only a smaller increase in size. Hence Assertion (A) is true.
3. Evaluating Reason (R):
   • The reason given is true. As we move down a group, the covalent and ionic radii generally increase due to the addition of electron shells.
4. Relationship Between Assertion (A) and Reason (R):
   • While both the assertion and the reason are true, (R) does not specifically explain the smaller increase from As to Bi due to poor shielding of f orbitals, which is crucial here.
5. Conclusion:
   • The most appropriate option is: "Both (A) and (R) are true but (R) is not the correct explanation of (A)." It correctly aligns with the given facts and trends.

Thus, the correct response is that while both statements are true, the reason does not adequately explain the assertion.

Answer 2

Step 1. Analyze the Assertion (A): The increase in covalent radius from N to P is significant due to additional electron shells. However, from A to B, the increase in size is smaller because of the presence of poor shielding by d- and f-electrons.

Step 2. Analyze the Reason (R): The statement in (R) is generally true as covalent and ionic radii tend to increase down the group in the periodic table. However, this reason does not specifically explain the smaller increase observed from A to B.

Step 3. Conclusion: Although both statements are individually true, the reason provided does not correctly explain the observed trend in covalent radii from A to B.