The number of electrons involved in the reduction of $Cr_2O_7^{2-}$ in acidic solution to $Cr^{3+}$ is

$2 MnO_{4}^{-} + b C_{2}O_{4}^{2-} + c H^{+} \rightarrow x Mn^{2+} + y CO_{2} + z H_{2}O$
If the above equation is balanced with integer coefficients,the value of $c$ is ...........
(Round off to the Nearest Integer).

The number of moles of $K_2Cr_2O_7$ reduced by $1 \, mol$ of $Sn^{2+}$ is:

How many moles of $H_2O_2$ are required to decolorize $1 \ mol$ of $KMnO_4$ in an acidic medium (in $.5$)?

Which of the following reactions involves oxidation-reduction?

Justify that the reaction: $2 Na ( s ) + H_2 ( g ) \rightarrow 2 NaH ( s )$ is a redox change.