Question

What is the correct order of the following elements with respect to their density ?

• A. Cr<Fe<Co<Cu<Zn
• B. Zn<Cr<Fe<Co<Cu
• C. Zn<Cu<Co<Fe<Cr
• D. Cr<Zn<Co<Cu<Fe

Hint:

Density = Mass / Volume. For 3d metals, the decrease in volume outweighs the increase in mass until you reach Zinc.

Answer 1

The Correct Option is B

Step 1: In the 3d transition series, density generally increases from left to right as atomic mass increases and atomic volume decreases.
Step 2: However, Zinc ($Zn$) is an exception; it has a larger atomic radius than the preceding transition metals because its 3d subshell is completely filled, leading to more electron-electron repulsion.
Step 3: Therefore, $Zn$ has a lower density than $Cr$. The correct increasing order is $Zn<Cr<Fe<Co<Cu$.