Oxidation reaction involves loss of electrons, and reduction reaction involves gain of electrons. The reaction in which a species disproportinates into two oxidation states ( lower and higher) is called disproportionation reaction.
Which of the following statements is correct?

Options

A. An element in the lowest oxidation state acts only as a reducing agent.
B. An element in the highest oxidation state acts only as a reducing agent.
C. The oxidation number of `V` is `Rb_(4)K(HV_(10)O_(28)) is +4`.
D. The oxidation number and valency of `Hg` in calomel is `+1`

Answer

A

Explanation

a. An element in the lowest oxidation state can only attain higher oxidation state. So it is a reductant and undergoes oxidation.
b. An element in the highest oxidation state only attain lower oxidation state. So it si an oxidant and undergoes reduction.
c. The oxidation state of `Rb` and `K` is `+1` ( first group element)
`overset(+1xx4+1)(Rb_(4)K(HV_(10)O_(28))^(-5)`
`HV_(10)O_(28)^(-5)=1+10x-2xx28= -5`
d. Calomel is `overset(+1xx2-1xx2)(Hg_(2)+Cl_(2))`
The oxidation number of `Hg` is `+1` and valency is `2`.