Question

Which of the following has the highest melting point?
Option-
A.$BeC{l_2}$
B.$MgC{l_2}$
C.$CaC{l_2}$
D.$BaC{l_2}$

Answer 1

Melting point of element is defined as a particular temperature at which solid as well as liquid phase of the same element can exist in equilibrium. Melting point is calculated for solid substances when they turn into liquid when particular heat is provided.

Complete answer:
Melting point of any substance changes with change in number of properties out of which size of the atom or element is the basic factor. As we see from the question alkaline earth metals form their respective chloride. Therefore, the size and shape of chlorine atoms is the same in all the given options so it does not affect the melting point of the compound.
In all the given options only the elements of group $\left( {IIA} \right)$ changes, therefore size of these elements has a significant effect on the melting point of the compound. We already know from the basic properties of the periodic table that as we move up to down in the same group, size of atoms increases due to increase in orbitals. As the size of alkaline earth metal increases, the total effective surface area of the compound increases and due to the large surface area a large amount of heat must be provided to melt the compound.
In the group $\left( {IIA} \right)$ elements, Barium comes in period $6$ and has maximum atomic size. Therefore, maximum heat must be required by $BaC{l_2}$ to melt it.
$\Rightarrow$$$BaC{l_2}$$ has the highest melting point.

Therefore, option $\left( D \right)$ is correct.

Note:
Other factors which influence the melting point of a substance are intermolecular forces present in the molecule, shape of the molecule, and presence or absence of ionic bond. Melting point of crystalline substances is always sharp and higher than amorphous solid.