Which one of the following reactions does not take place?

$X$ and $Y$ are the number of electrons involved, respectively, during the oxidation of $I^{-}$ to $I_{2}$ and $S^{2-}$ to $S$ by acidified $K_{2}Cr_{2}O_{7}$. The value of $X + Y$ is . . . . . . .

Given below are two statements :-
Statement $I$ :- In redox titration,the indicators used are sensitive to change in $pH$ of the solution.
Statement $II$ :- In acid-base titration,the indicators used are sensitive to change in oxidation potential.
In the light of the above statements,choose the most appropriate answer from the options given below.

When hypo solution is added to cupric sulphate solution,the blue colour of the latter is discharged,due to the formation of:

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$BaCO_3 \downarrow + 2CH_3COOH \longrightarrow Ba(CH_3COO)_2 + CO_2 \uparrow + H_2O$

When $SO_2$ gas is passed through an acidified solution of $K_2Cr_2O_7$,the solution turns........