If stoichiometric quantities of a $KMnO_4$ and $K_2Cr_2O_7$ mixture are added for the oxidation of $Fe^{2+}$ to $Fe^{3+}$ in an acidic medium,then $Fe^{2+}$ will be oxidized:

Which of the following is a true statement?

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

Which of the following are non-metal displacement reactions?
$(A)$ $Ca_{(s)} + 2 H_2 O_{(l)} \longrightarrow Ca(OH)_{2(aq)} + H_{2(g)}$
$(B)$ $V_2 O_{5(s)} + 5 Ca_{(s)} \stackrel{\Delta}{\longrightarrow} 2 V_{(s)} + 5 CaO_{(s)}$
$(C)$ $2 Fe_{(s)} + 3 H_2 O_{(g)} \stackrel{\Delta}{\longrightarrow} Fe_2 O_{3(s)} + 3 H_{2(g)}$
$(D)$ $Cr_2 O_{3(s)} + 2 Al_{(s)} \stackrel{\Delta}{\longrightarrow} Al_2 O_{3(s)} + 2 Cr_{(s)}$

When mercury $(II)$ chloride is treated with excess of stannous chloride,the products obtained are

$Fe^{3+}$ is reduced to $Fe^{2+}$ by using:
$A$. $H_2O_2$ in presence of $NaOH$
$B$. $Na_2O_2$ in water
$C$. $H_2O_2$ in presence of $H_2SO_4$
$D$. $Na_2O_2$ in presence of $H_2SO_4$