Question

In which of the following reactions, there is no change in valency?
A. $4KCl{{O}_{3}}\to 3KCl{{O}_{4}}+KCl$
B. $S{{O}_{2}}+{{H}_{2}}S\to 2{{H}_{2}}O+3S$
C. $Ba{{O}_{2}}+{{H}_{2}}S{{O}_{4}}\to BaS{{O}_{4}}+{{H}_{2}}{{O}_{2}}$
D. $3Ba{{O}_{2}}+{{O}_{2}}\to 2Ba{{O}_{2}}$

Answer 1

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:
Valency of any compound is generally calculated by knowing the oxidation state of that atom. The oxidation number also known as oxidation state which describes the degree of oxidation i.e, loss of electrons of an atom in a chemical compound. Conceptually the oxidation state may be positive, negative or zero.
Here we have to take a look in which the oxidation state becomes constant as in this way we can say that valency of that atom also remains the same. In option A the oxidation state of potassium atom changes, equation B oxidation state of sulphur atom also changes, equation C the oxidation state of barium atom remains same i.e. -1 in both cases in reactant as well as product and in equation D the oxidation state of barium atom changes.

Thus, we can say that option C is the correct answer.

Note:
Oxidation is defined as the loss of electrons or we can say that increase in the oxidation state of an atom, ion or molecule while reduction can be defined as the gain of electrons or decreases in the oxidation state of any given atom, ion or molecule.