Question

In bisulfite ion, the formal charge on sulphur atom is:
A. +1
B. +2
C. +4
D. +6

Answer 1

Hint: Valence electrons can be defined as the electrons present in the outer shell of an atom which can participate in the formation of chemical bonds and this combining capacity of any atom is known as valency of that atom.

Complete answer:
Valence electrons can be calculated with the help of electronic configuration of an atom like the electrons present in the outermost shell. To know about this we first have to know the concept of electronic configuration. In this we fill the electrons according to three known rules called Aufbau principle, Pauli Exclusion Principle and Hund’s rule which describes how electrons are filled step by step. Like in s subshell only 2 electrons can be filled, in p subshell at most 6 electrons, d subshell 10 electrons and in f subshell only 14 electrons are present.
Formal charge is generally known as the charge produced on the compound and formal charge can be calculated by the formula
$Total\ \text{number of valence electrons - }\dfrac{1}{2}(tota\operatorname{l}\ number\ \text{of shared electrons)}$
We know that the chemical formula shown by bisulphite ion is $HS{{O}_{4}}^{-}$where we know that Sulphur atom has 6 valence electrons in its outermost shell and the electrons shared in the compound is 8 so by putting the values in equation we find that
Formal charge = $6\text{ - }\dfrac{1}{2}(8\text{)=6-4=2}$

Hence option B is the correct answer.

Note:
Here some of you may do wrong during calculating the formal charge by considering lone pairs of electrons as one electron. But always keep in mind we have to count each non bonded electron separately, not in pairs.