Question

Which of the following shows least melting point?

• A. $Be$
• B. $Mg$
• C. $Ca$
• D. $Sr$

Answer 1

The correct option is B $Mg$

Ans : $B$ $\to$ $Mg$

Generally melting point of the metals decreases down the group. But $Mg$ has anomalously low melting point in group $2$.

Group $2$ metals have metallic bonding. If we look at the crystal structure, $Be$ & $Mg$ are hexagonal close packed, $Ca$ & $Sr$ are face centered cubic.

At melting point, $Be$, $Ca$ and $Sr$ are body centered where as $Mg$ is hexagonal closed packed. Due to this arrangement, $Mg$ shows least melting point