Mg
Si
Na
Al
The correct option is B Mg
Elements of group Na form XCl halide.
Elements of group Mg form XCl2 halide.
Elements of group Al form XCl3 halide.
Elements of group Si form XCl4 halide.
As element X forms a chloride with the formula XCl2, which is solid with a high melting point, X would most likely be in the same group of Mg.