A solution of $$KMn{O_4}$$ is reduced to various products depending upon its $$pH.$$ At $$pH < 7$$ it is reduced to a colourless solution $$\left( A \right),$$ at $$pH=7$$ it gives a green solution $$(C). (A), (B)$$ and $$(C)$$ are

$$(A)$$ $$(B)$$ $$(C)$$

(a) $$M{n^{2 + }}$$ $$Mn{O_2}$$ $$MnO_4^{2 - }$$

(b) $$Mn{O_2}$$ $$M{n^{2 + }}$$ $$MnO_4^{2 - }$$

(c) $$M{n^{2 + }}$$ $$MnO_4^{2 - }$$ $$Mn{O_2}$$

(d) $$MnO_4^{2 - }$$ $$M{n^{2 + }}$$ $$Mn{O_2}$$

Question

A solution of $$KMn{O_4}$$ is reduced to various products depending upon its $$pH.$$ At $$pH < 7$$ it is reduced to a colourless solution $$\left( A \right),$$ at $$pH=7$$ it gives a green solution $$(C). (A), (B)$$ and $$(C)$$ are

$$(A)$$ $$(B)$$ $$(C)$$

(a) $$M{n^{2 + }}$$ $$Mn{O_2}$$ $$MnO_4^{2 - }$$

(b) $$Mn{O_2}$$ $$M{n^{2 + }}$$ $$MnO_4^{2 - }$$

(c) $$M{n^{2 + }}$$ $$MnO_4^{2 - }$$ $$Mn{O_2}$$

(d) $$MnO_4^{2 - }$$ $$M{n^{2 + }}$$ $$Mn{O_2}$$

	$$(A)$$	$$(B)$$	$$(C)$$
(a)	$$M{n^{2 + }}$$	$$Mn{O_2}$$	$$MnO_4^{2 - }$$
(b)	$$Mn{O_2}$$	$$M{n^{2 + }}$$	$$MnO_4^{2 - }$$
(c)	$$M{n^{2 + }}$$	$$MnO_4^{2 - }$$	$$Mn{O_2}$$
(d)	$$MnO_4^{2 - }$$	$$M{n^{2 + }}$$	$$Mn{O_2}$$

A. (a)

B. (b)

C. (c)

D. (d)

Answer : (a)

Solution :
$${\text{At}}\,pH < 7,{\text{in acidic medium}}$$
$$MnO_4^ - + 8{H^ + } + 5{e^ - } \to $$ $$\mathop {M{n^{2 + }}}\limits_{{\text{(colourless)}}} + 4{H_2}O$$
$${\text{At}}\,pH = 7,{\text{in neutral medium}}$$
$${\text{MnO}}_4^ - + 2{H_2}O + 3{e^ - } \to $$ $$\mathop {Mn{O_2} + }\limits_{{\text{(brown precipitate)}}} 4O{H^ - }$$
$${\text{At}}\,pH > 7,{\text{in alkaline medium}}$$
$$MnO_4^ - + {e^ - } \to \mathop {MnO_4^{2 - }}\limits_{{\text{(green)}}} $$