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

Step 1: Read the assertion.
Assertion A: 3d transition metals generally have high melting points.
Step 2: Judge the assertion.
Transition metals like Cr, Fe, Co and Ni show high melting points because of strong metallic bonding, so Assertion A is true.
Step 3: Read the reason.
Reason R: both 3d and 4s electrons take part in the interatomic metallic bonding.
Step 4: Judge the reason.
These metals have partially filled d-orbitals; the delocalised d-electrons add to the bonding alongside the s-electrons, so Reason R is true.
Step 5: Test whether R explains A.
More delocalised electrons mean stronger metallic bonds, a higher enthalpy of atomisation, and therefore higher melting points. So R directly explains A.
Step 6: Conclude.
Both correct and R is the correct explanation of A.
\[ \boxed{\text{Both A and R are correct and R is the correct explanation of A.}} \]