Question

The correct option with order of melting points of the pairs (Mn, Fe), (Tc, Ru) and (Re, Os) is:

• A. Fe < Mn, Ru < Tc and Re < Os
• B. Mn < Fe, Tc < Ru and Os < Re
• C. Mn < Fe, Tc < Ru and Re < Os
• D. Fe < Mn, Ru < Tc and Os < Re

Hint:

In general, elements in the same group or period have comparable melting points, but this can vary based on electron configuration and atomic structure.

Answer 1

The Correct Option is C

The question involves determining the order of melting points for pairs of elements (Mn, Fe), (Tc, Ru), and (Re, Os). We have four options to consider. Let's analyze each pair:

1. Mn (Manganese) and Fe (Iron):
   Manganese has a lower melting point compared to Iron. Therefore, Mn < Fe.
2. Tc (Technetium) and Ru (Ruthenium):
   Technetium, being in the same column group earlier than Ruthenium, has a lower melting point. Thus, Tc < Ru.
3. Re (Rhenium) and Os (Osmium):
   Rhenium has a lower melting point compared to Osmium, so Re < Os.

Based on the analysis, the correct order of the melting points is Mn < Fe, Tc < Ru and Re < Os. 

This corresponds to the correct option given: Mn < Fe, Tc < Ru and Re < Os

Answer 2

Step 1: Understand the concept.
The melting point of transition metals depends mainly on the strength of metallic bonding, which arises due to the participation of (n−1)d and ns electrons in bond formation. The number of unpaired d-electrons significantly affects metallic bonding strength — more unpaired electrons mean stronger metallic bonds and thus higher melting points.

Step 2: Analyze each pair.
(A) (Mn, Fe)
- Manganese (Mn) has the electronic configuration [Ar] 3d⁵ 4s², with a half-filled d-subshell. Due to its stable configuration, the metallic bonding is weaker, resulting in a relatively lower melting point.
- Iron (Fe) has [Ar] 3d⁶ 4s², allowing more delocalized electrons to participate in bonding, leading to stronger metallic bonds.
Thus, Mn < Fe.

(B) (Tc, Ru)
- Technetium (Tc) and Ruthenium (Ru) belong to the same group (Group 7 and 8 respectively) in the second transition series.
- Ruthenium (Ru) has a higher number of unpaired d-electrons available for metallic bonding than Tc, resulting in a stronger metallic bond.
Hence, Tc < Ru.

(C) (Re, Os)
- Rhenium (Re) and Osmium (Os) belong to the third transition series (5d block).
- Osmium (Os) has more unpaired d-electrons and forms stronger metallic bonds than Rhenium (Re).
Therefore, Re < Os.

Step 3: Conclusion.
The correct order of melting points based on metallic bonding strength is:
\[ \boxed{\text{Mn < Fe, Tc < Ru, and Re < Os}} \]