How many protons will be consumed when dichromate ion oxidises $Fe^{2+}$ ions in aqueous acidic medium?

Assertion : When a metal is treated with conc. $HNO_3$,it generally yields a nitrate,$NO_2$,and $H_2O$.
Reason : Conc. $HNO_3$ reacts with a metal and first produces a metal nitrate and nascent hydrogen. The nascent hydrogen then further reduces $HNO_3$ to $NO_2$.

How many grams of $Mg$ is required to completely reduce $100 \ mL$ of $0.1 \ M$ $NO_3^{-}$ solution using the following reaction:
$NO_3^{-} + Mg \longrightarrow Mg^{2+} + NH_3$

Balance the following redox reactions by the ion-electron method:
$(a)$ $MnO_4^-(aq) + I^{-}(aq) \rightarrow MnO_2(s) + I_2(s)$ (in basic medium)
$(b)$ $MnO_4^-(aq) + SO_2(g) \rightarrow Mn^{2+}(aq) + HSO_4^-(aq)$ (in acidic solution)
$(c)$ $H_2O_2(aq) + Fe^{2+}(aq) \rightarrow Fe^{3+}(aq) + H_2O(l)$ (in acidic solution)
$(d)$ $Cr_2O_7^{2-} + SO_2(g) \rightarrow Cr^{3+}(aq) + SO_4^{2-}(aq)$ (in acidic solution)

Assign $A, B, C, D$ from the given type of reaction.
$Ba(OH)_2 + SO_2 \longrightarrow BaSO_3 \downarrow + H_2O$

$2 IO_3^- + x I^- + 12 H^+ \rightarrow 6 I_2 + 6 H_2 O$. What is the value of $x$?