In balancing the half-reaction $S_2O_3^{2-} \to S_{(s)}$,the number of electrons that must be added is:

In mildly alkaline medium,thiosulphate ion is oxidized by $MnO_4^-$ to $A$. The oxidation state of sulphur in $A$ is ..... .

Chlorine is used to purify drinking water. Excess of chlorine is harmful. The excess of chlorine is removed by treating with sulphur dioxide. Present a balanced equation for this redox change taking place in water.

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

For the reaction:
$I^{-} + ClO_{3}^{-} + H_{2}SO_{4} \longrightarrow Cl^{-} + HSO_{4}^{-} + I_{2}$
The correct statement$(s)$ in the balanced equation is/are:
$A$. Stoichiometric coefficient of $HSO_{4}^{-}$ is $6$.
$B$. Iodide is oxidized.
$C$. Sulphur is reduced.
$D$. $H_{2}O$ is one of the products.

The heating of $(NH_4)_2Cr_2O_7$ produces another chromium compound along with $N_2$ gas. The change of the oxidation state of $Cr$ in the reaction is