Which of the following can react with $K_{2}Cr_{2}O_{7}$?

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$Ca(OH)_2 + CO_2 \longrightarrow CaCO_3 \downarrow + H_2O$

To an acidified dichromate solution,a pinch of $Na_2O_2$ is added and shaken. What is observed?

Identify the substance oxidised,reduced,oxidising agent,and reducing agent for each of the following reactions:
$(a)$ $2AgBr_{(s)} + C_6H_6O_{2(aq)} \to 2Ag_{(s)} + 2HBr_{(aq)} + C_6H_4O_{2(aq)}$
$(b)$ $HCHO_{(l)} + 2[Ag(NH_3)_2]^+_{(aq)} + 3OH^-_{(aq)} \to 2Ag_{(s)} + HCOO^-_{(aq)} + 2NH_{3(aq)} + 2H_2O_{(l)}$
$(c)$ $HCHO_{(l)} + 2Cu^{2+}_{(aq)} + 5OH^-_{(aq)} \to Cu_2O_{(s)} + HCOO^-_{(aq)} + 3H_2O_{(l)}$
$(d)$ $N_2H_{4(l)} + 2H_2O_{2(l)} \to N_{2(g)} + 4H_2O_{(l)}$
$(e)$ $Pb_{(s)} + PbO_{2(s)} + 2H_2SO_{4(aq)} \to 2PbSO_{4(s)} + 2H_2O_{(l)}$

Given below are two statements.
Statement-$I$: In the decomposition of potassium chlorate,$Cl$ is reduced.
Statement-$II$: Reaction of $Na$ with $O_2$ to form $Na_2O$ is a redox reaction.
The correct answer is

$H_2O_2$ reduces $KMnO_4$ in acidic medium to '$x$' and in basic medium to '$y$'. What are $x$ and $y$?