Question

Valency of sulphur in \[{\rm{N}}{{\rm{a}}_{\rm{2}}}{{\rm{S}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}\] is
A) Two
B) Three
C) Four
D) Six

Answer 1

Hint: The word valency defines an atom's combining capacity. In general meaning, valency means the count of electrons that an atom gains or donates to attain stability and achieve noble gas configuration.

Complete step by step solution:Let's find out the valency of the sulphur atom in \[{\rm{N}}{{\rm{a}}_{\rm{2}}}{{\rm{S}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}\]. For that, we need to know the oxidation states of sodium and oxygen.

Let's discuss how we know the oxidation states or valency of sodium atoms.
We know, sodium has an atomic number of 11. So, its electronic configuration would be 2,8,1. So, to attain the stability, it can lose one electron. Thus, it may achieve noble gas configuration. So, sodium atoms have a valency of +1.

Now, we will understand the valency of the oxygen atom. Oxygen's atomic atomic number is 8. So, its configuration is 2,6. So, to attain stability, it can accept two numbers of electrons. Therefore, its valency is -2.

Now, we will find out the valency of Sulphur. Let's take the valency of sulphur as x, and oxygen's valency is -2 and sodium's valency is +1. And we know, summation of the valencies of atoms in a compound is zero.

\[2 \times 1 + 2 \times x + 3 \times ( - 2) = 0\]
\[2 + 2x - 6 = 0\]
\[2x - 4 = 0\]
 \[2x = 4\]
\[x = 2\]

So, the sulphur atoms have a valency of 2.

Hence, option A is right.

Note: Always remember that the atom of Oxygen has multiple oxidation states. In most of the oxides, its oxidation state is -2. In case of peroxides, its oxidation state is -1 and in case of dioxygen difluoride, its oxidation state is +1.