Question

$KMn{O_4}$ in acidic medium is always reduced to $M{n^{2 + }}$
A. True
B. False

Answer 1

When potassium is added to an acidic solution, the permanganate (VII) is reduced to its (pale pink) $+ 2$ oxidation state. Also, the oxidation number decreases by $5$.

Complete step by step answer: There are acid-base theories consisting of concepts like Bronsted-Lowry theory, Arrhenius acid-base concept, and Lewis theory. The Bronsted-Lowry theory states that some substances act as acids or bases when they are dissolved in solvents other than water, such as liquid ammonia. This theory describes the acids as the proton donors and the bases as proton acceptors. The reason behind it is that a hydrogen atom contains one proton and one electron. So, an ${H^ + }$ ion is simply called a proton and acids donate this ${H^ + }$ ion to bases. So, acids are proton donors and bases are proton acceptors.
Now, when potassium is added to an acidic solution, the permanganate (VII) is reduced to its (pale pink) $+ 2$ oxidation state of the manganese (III) $\left( {M{n^{2 + }}} \right)$ ion.
$8{H^ + } + Mn{O^{4 - }} + 5{e^ - } \to M{n^{2 + }} + 4{H_2}O$
In a strongly basic solution, we can also see that the permanganate (VII) is reduced to the (green) $+ 6$ oxidation state of the manganate ion $\left( {MnO_2^{4 - }} \right)$ :
$Mn{O^{4 - }} + {e^ - } \to MnO_2^{4 - }$
But, in a neutral medium, this compound gets reduced to the (brown) $+ 4$ oxidation state of manganese dioxide $\left( {Mn{O_2}} \right)$.
So, the statement is true.
So, the correct answer is “Option A”.

Note:
The Lewis theory defines an acid as a compound, which can accept a pair of electrons and in contrast, it defines the base as a compound, which can donate a pair of electrons. For example, boron trifluoride, $B{F_3}$, can be considered as a Lewis acid and ethyl alcohol can be considered as a Lewis base. Again, the Arrhenius theory explains that an acid is a compound that can dissolve into the water to produce hydrogen ions, ${H^ + }$, and a base is a compound, which can dissolve into the water to produce hydroxide ions, $O{H^ - }$. For example, hydrochloric acid, $HCl$, dissociates in water to yield the required hydrogen ions, ${H^ + }$, and also chloride ions, $C{l^ - }$. The base, sodium hydroxide, $NaOH$, dissociates in water to give the required hydroxide ions, $O{H^ - }$, together with sodium ions, $N{a^ + }$.
When $KMn{O_4}$ acts as an oxidizing agent in an acidic medium, the oxidation number of manganese decreases from $+ 7$ to $+ 2$. Thus, the oxidation number decreases by $5$.