Which of the following is not formed when $H_2S$ reacts with acidic $K_2Cr_2O_7$ solution?

Which one is the oxidising agent in the reaction below?
$2CrO_4^{2-} + 2H^{+} \to Cr_2O_7^{2-} + H_2O$

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$Na_2CrO_4 + AgF \longrightarrow Ag_2CrO_4 \downarrow + NaF$

$I^{-}(aq.) + MnO_4^{-}(aq.) \xrightarrow{H^{+}} X + Mn^{2+}(aq.)$
$I^{-}(aq.) + MnO_4^{-}(aq.) \xrightarrow{\text{Neutral or weakly } OH^{-}} Y + MnO_2$
$MnO_4^{-}(aq.) + Mn^{2+}(aq.) \xrightarrow{ZnSO_4} Z + 4H^{+}$
Products $X, Y$ and $Z$ are respectively :

Whenever a reaction between an oxidising agent and a reducing agent is carried out,a compound of lower oxidation state is formed if the reducing agent is in excess and a compound of higher oxidation state is formed if the oxidising agent is in excess. Justify this statement giving three illustrations.

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$Na_3PO_4 + Fe_2(SO_4)_3 \longrightarrow FePO_4 \downarrow + Na_2SO_4$