Question

Which element from following is a soft element?

• A. $\mathrm{Mn}$
• B. $\mathrm{Zn}$
• C. $\mathrm{Co}$
• D. $\mathrm{Ni}$

Hint:

Group 12 elements ($\mathrm{Zn}$, $\mathrm{Cd}$, $\mathrm{Hg}$) have a completely filled $\mathrm{d}$ subshell ($\mathrm{d^{10}}$). This limits their metallic bonding capability, making them much softer and giving them drastically lower melting and boiling points compared to neighboring transition metals.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks us to identify the relatively "soft" metallic element from the provided choices ($\mathrm{Mn}$, $\mathrm{Zn}$, $\mathrm{Co}$, $\mathrm{Ni}$).

Step 2: Key Formula or Approach:
Transition metals typically exhibit high hardness due to the participation of both outer $\mathrm{s}$ and inner $\mathrm{d}$ electrons in metallic bonding, which creates a strong, rigid crystal lattice. Elements with a fully filled $\mathrm{d}$ subshell ($\mathrm{d^{10}}$) cannot engage their $\mathrm{d}$ electrons in covalent metallic bonding, resulting in significantly weaker metallic interactions and lower mechanical hardness.

Step 3: Detailed Explanation:
Let's look at the electronic configurations of the given elements:

• Manganese ($\mathrm{Mn}$, $Z=25$): $[\mathrm{Ar}]\,3d^5\,4s^2$ — Hard and brittle.

• Cobalt ($\mathrm{Co}$, $Z=27$): $[\mathrm{Ar}]\,3d^7\,4s^2$ — Quite hard and strong.

• Nickel ($\mathrm{Ni}$, $Z=28$): $[\mathrm{Ar}]\,3d^8\,4s^2$ — Tough, ductile, and hard.

• Zinc ($\mathrm{Zn}$, $Z=30$): $[\mathrm{Ar}]\,3d^{10}\,4s^2$ — Has a completely filled $3d$ subshell.
Because Zinc's $3d$ electrons are entirely filled and tightly bound to its nucleus, they do not participate in metallic bonding. Metallic bonding in zinc is mediated almost entirely by its two $4s$ electrons. This weak metallic binding force makes Zinc significantly softer, more malleable, and less dense than standard transition elements like $\mathrm{Mn}$, $\mathrm{Co}$, and $\mathrm{Ni}$.

Step 4: Final Answer:
The soft element among the choices is $\mathrm{Zn}$, which corresponds to option (B).