Question

The molecular formula of Mercury (II) chloride is:
(A) HgCl
(B) $Hg_2Cl_2$
(C) $HgCl_3$
(D) $HgCl_2$

Answer 1

Hint: Find the cations and anions required to obtain Mercury (II) chloride.

Complete step by step answer:
A molecule is formed from cations and anions. Cations are the elements which have net positive charge due to lack of electrons whereas anions have net negative charge because they have more electrons than protons. In Mercury (II) chloride cation is $Hg^{+2}$ whereas anion is $ Cl^{-1}$. The reaction is as follows
$Hg^{+2} +2Cl^{-1} \Rightarrow HgCl_2$

Here $ Cl^{-1}$ can only donate 1 electron whereas $Hg^{+2}$ requires 2 electrons in outer shell for stability, So two $ Cl^{-1}$ elements are chemically bonded with $Hg^{+2}$ to form Mercury (II) chloride.
Hence the correct answer is (D) $HgCl_2$.

Additional information:
In question Mercury (II) chloride is mentioned that means the valency of mercury is given as 2. From that we can know how many chlorine ions should be taken to maintain stability of the molecule. In this case mercury requires electrons to attain stability and 2 chlorine ions can give 2 electrons. Finally $HgCl_2$ molecule is formed.

Note: A student may get confused by other names of Mercury (II) chloride. The other names are mercury dichloride, mercuric chloride, corrosive sublimate.