Question

White $Mn{\left( {OH} \right)_2}$ becomes a green coloured compound on reaction with sodium peroxide.
A. Because of the formation of manganate ions.
B. Because of the formation of $Mn{\left( {OH} \right)_2}$
C. Because of the formation of ions $4M{n^{2 + }}$.
D. Because of the formation of permanganate ions.

Answer 1

When white manganese hydroxide reacts with sodium peroxide to form green colour compound as shown
$Mn{\left( {OH} \right)_2} + {H_2}{O_2} \to M{n_2}{O_3} + {H_2}O$
This is because of the formation of $4M{n^{2 + }}$. We will see this clearly when we will balance the equation that there is a formation .

Complete step-by-step answer: Manganese is a grey or reddish white metal this metal is very hard and brittle.it is one of those metals which readily dissolves in dilute acids.
Sodium peroxide is an inorganic compound with the formula .This is a yellowish coloured compound and this is obtained when sodium is burnt in excess of oxygen. It is a strong base.
When white manganese hydroxide reacts with sodium peroxide to form green colour compound as shown
$Mn{\left( {OH} \right)_2} + {H_2}{O_2} \to M{n_2}{O_3} + {H_2}O$
This is because of the formation of $4M{n^{2 + }}$. We will see this clearly when we will balance the equation that there is a formation .

Additional information: Manganese hydroxide is also called pyrochroite. It is a white solid although samples darken quickly upon exposure to air owing to oxidation . also, it is poorly soluble in water.

Hence, option C is correct which states that Because of the formation of ions $4M{n^{2 + }}$. The compound turns green in colour.

Note: Manganese hydroxide precipitates as a solid when an alkali metal hydroxide is added to an aqueous solution of manganese salt.It is also indicated as the darkening sample as already explained.