Question

hen $Mn{O}_2$ is fused with $KOH$ and $KN{O}_3$ a colored compound is formed the product and its color is :
A. $K_{2}Mn{O}_4,$ Green .
B. $KMn{O}_4$, Purple
C. $M{N}_2{O}_3$, Blue
D. $K_{3}Mn{O}_2$, Red

Answer 1

Hint: Whenever $Mn{O}_2$ is made to fuse with $KOH$ and $KN{O}_3$ , a purple – green colored compound known as potassium manganate is formed which is known to treat skin infections including the fungal infections.

Complete step by step answer: $Mn{O}_2$ , this is known as manganese dioxide and is an inorganic compound of blackish or brown color.
$Mn{O}_2$ is a weakly acidic and mildly basic substance and we can somewhat call it an amphoteric substance too.
$KOH$ is potassium hydroxide . It usually becomes tacky in air as it is hygroscopic in nature.
$KN{O}_3$ is called potassium nitrate which is a strong oxidizer used in making fertilizers , medicines etc.
The reaction of $Mn{O}_2$ with $KOH$ and $KN{O}_3$ leads to the production of compound $K_{2}Mn{O}_4$ known as potassium manganate.
The involved reaction is :
$Mn{O}_2+KN{O}_3+KOH\underset{KN{O}_2}{\overset{350-{450}^{\circ }c}{\to }}{K}_{2}Mn{O}_4+H_{2}O$
$K_{2}Mn{O}_4$ is the main product known as potassium manganate that is of green color.
The manganate salts get readily disproportionate to permanganate ions and manganese dioxide. The reaction equation can be written as:
$\text{3}{\text{K}}_{\text{2}}\text{Mn}{\text{O}}_{\text{4}}\text{ + 2}{\text{H}}_{\text{2}}\text{O}\to \text{2KMn}{\text{O}}_{\text{4}}\text{ + Mn}{\text{O}}_{\text{2}}\text{ + 4KOH}$
The manganate/manganate (IV) pair is referred to as a chemical chameleon. The reason behind is the colorful nature of disproportionation.
This green-colored salt is used as an intermediate in the industrial synthesis of potassium permanganate.
Hence , the option A is the correct one.

Note: The above mentioned reaction in the question should take place in appropriate reaction conditions, that is , it requires a temperature condition of ${350}^{\circ }-{450}^{\circ }c$ . Potassium manganate and potassium permanganate should not be mixed up. Both of the compounds have different chemical formulas and even different chemical properties.