$50 \ mL$ of $0.1 \ M$ solution of a salt reacted with $25 \ mL$ of $0.1 \ M$ solution of sodium sulphite. The half-reaction for the oxidation of sulphite ion is:
$SO_{3}^{2-} (aq) + H_{2}O (l) \to SO_{4}^{2-} (aq) + 2H^{+} (aq) + 2e^{-}$
If the oxidation number of the metal in the salt was $+3$,what would be the new oxidation number of the metal?

Balance the following equations in basic medium by the ion-electron method and identify the oxidising agent and the reducing agent.
$(a)$ $P_{4(s)} + OH^{-}_{(aq)} \rightarrow PH_{3(g)} + H_{2}P{O_{2}}^{-}_{(aq)}$
$(b)$ $N_{2}H_{4(l)} + Cl{O_{3}}^{-}_{(aq)} \rightarrow NO_{(g)} + Cl^{-}_{(g)}$
$(c)$ $Cl_{2}O_{7(g)} + H_{2}O_{2(aq)} \rightarrow Cl{O_{2}}^{-}_{(aq)} + O_{2(g)} + H^{+}_{(aq)}$

$200 \ mL$ of $x \times 10^{-3} \ M$ potassium dichromate $(K_2Cr_2O_7)$ is required to oxidise $750 \ mL$ of $0.6 \ M$ Mohr's salt $(FeSO_4 \cdot (NH_4)_2SO_4 \cdot 6H_2O)$ solution in acidic medium. Here $x =$ ?

Which of the following reactions is a decomposition redox reaction?

$A$ copper coin is completely covered with a gold film and is placed in dilute $HNO_3$. This will result in the formation of:

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$BaSO_3(s) + H_2SO_4(aq) \longrightarrow BaSO_4(s) + SO_2(g) + H_2O(l)$