Acidified $K_2Cr_2O_7$ solution turns green when $Na_2SO_3$ is added to it. This is due to the formation of

Consider the following reaction:
$MnO_2 + KOH + O_2 \rightarrow A + H_2O$
Product '$A$' in neutral or acidic medium disproportionates to give products '$B$' and '$C$' along with water. The sum of spin-only magnetic moment values of '$B$' and '$C$' is . . . . . $BM$. (nearest integer)
(Given atomic number of $Mn$ is $25$)

What is the equivalent weight of the reductant in the reaction $2[Fe(CN)_6]^{3-} + H_2O_2 + 2OH^{-} \rightarrow 2[Fe(CN)_6]^{4-} + 2H_2O + O_2$? (Given: $Fe = 56, C = 12, N = 14, O = 16, H = 1$)

The pair of compounds that can exist together is

Which of the following is not an intramolecular redox reaction?

$A$ solution of $KMnO_4$ on reduction yields either a colourless solution,a brown precipitate,or a green solution depending on the $pH$ of the solution. What different stages of the reduction do these represent and how are they carried out?