Question

Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R. Assertion A : Generally, 3d transition metals have high melting points. Reason R : Involvement of 3d-electrons in addition to 4s-electrons in the interatomic metallic bonding. In the light of the above statements, choose the most appropriate answer from the options given below.

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

Hint:

The greater the number of delocalized electrons participating in metallic bonding, the stronger the metallic bond and the higher the melting point. For transition metals, both \(ns\) and \((n-1)d\) electrons contribute to bonding.

Answer 1

The Correct Option is B

Concept: Transition metals exhibit characteristic metallic properties such as:

• High melting points

• High boiling points

• High enthalpy of atomization

• High density
These properties arise due to strong metallic bonding. Unlike alkali metals, transition metals possess both \(ns\) and \((n-1)d\) electrons that participate in metallic bonding.

Step 1: Examine Assertion A. Assertion states: Generally, 3d transition metals have high melting points. This statement is correct. Examples: \[ Cr,\ Fe,\ Co,\ Ni \] possess very high melting points because of strong metallic bonding. Therefore Assertion A is true.

Step 2: Examine Reason R. Reason states: 3d electrons along with 4s electrons participate in metallic bonding. This is also correct. Transition metals contain partially filled d-orbitals. These d-electrons become delocalized and contribute significantly to metallic bond formation. Hence the metallic bonding becomes much stronger than in s-block metals. Therefore Reason R is true.

Step 3: Determine whether R explains A. Because both 3d and 4s electrons contribute to metallic bonding: Strength of metallic bonding increases which results in: Higher enthalpy of atomization and consequently Higher melting points Thus the reason directly explains the assertion.

Step 4: Final conclusion. Assertion A is correct. Reason R is correct. Reason R correctly explains Assertion A. Therefore, \[ \boxed{\text{Option (B)}} \]