An element X forms a chloride with the formula $XC{{l}_{2}}$ , which is solid with a high melting point. X would most likely to be in the same group of the Periodic table as:
(A) Na
(B) Mg
(C) Al
(D) Si

Hint: The compound formed by the element X is $XC{{l}_{2}}$, which means that X must have a valency as +2. So, it must belong to group 2.

Complete step by step solution:
-We will start by calculating the valency of elements given in the option,
(i) Sodium (Na) has the atomic number as 11. The electronic configuration of sodium is
$1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{1}}$
Hence, it is clear that the valency of sodium is +1.
Therefore, sodium when combined with chlorine can form only XCl.

(ii) Magnesium (Mg) has the atomic number as 12. The electronic configuration of magnesium is
$1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}$
Hence, it is clear that the valency of magnesium is +2.
Therefore, magnesium when combined with chlorine can only form $XC{{l}_{2}}$ .

(iii) Aluminium (Al) has the atomic number as 13. The electronic configuration of aluminium is
$1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{3}}$
Hence, it is clear that the valency of aluminium is +3.
Therefore, aluminium when combined with chlorine can only form $XC{{l}_{3}}$ .

(iv) Silicon (Si) has the atomic number as 14. The electronic configuration of silicon is
$1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{4}}$
Hence, it is clear that the valency of silicon is +4.
Therefore, silicon, when combined with chlorine, can only form $XC{{l}_{4}}$ .

Hence the correct answer is option B.

Note: The temperature at which the vapour pressure of the liquid is equal to the external pressure surrounding the liquid is known as boiling point. The elements in the periodic table do follow a trend of the boiling table along with the group. Different groups show different trends in their boiling and melting point. Since the elements of our interest belong to the second period, let us see the trend of the second period. For group 2 elements, the boiling and melting points decrease as we move down the group.