Can titrations with $KMnO_4$ be performed in the presence of $HCl$? Why?

Compounds that should not be used as primary standards in titrimetric analysis are $:$
$A.$ $Na_2Cr_2O_7$
$B.$ Oxalic acid
$C.$ $NaOH$
$D.$ $FeSO_4 \cdot 6H_2O$
$E.$ Sodium tetraborate
Choose the most appropriate answer from the options given below $:$

Which reagent is commonly used in titration to determine the hardness of water?

Which of the graphs shown below would best represent the change in conductance $(G_{sol})$ when a solution containing $0.1 \, M$ each of $HCl$ and $HCN$ is titrated with $0.1 \, M$ $NaOH$ solution?

Solution $X$ contains $Na_2CO_3$ and $NaHCO_3$. $20 \ mL$ of $X$ when titrated using methyl orange indicator consumed $60 \ mL$ of $0.1 \ M \ HCl$ solution. In another experiment,$20 \ mL$ of $X$ solution when titrated using phenolphthalein consumed $20 \ mL$ of $0.1 \ M \ HCl$ solution. The concentrations (in $mol \ L^{-1}$) of $Na_2CO_3$ and $NaHCO_3$ in $X$ are respectively:

$20 \, mL$ of $0.02 \, M$ hypo solution is used for the titration of $10 \, mL$ of copper sulphate solution,in the presence of excess of $KI$ using starch as an indicator. The molarity of $Cu^{2+}$ is found to be $\times 10^{-2} \, M$ [nearest integer]. Given: $2 Cu^{2+} + 4 I^{-} \rightarrow Cu_{2}I_{2} + I_{2}$ and $I_{2} + 2 S_{2}O_{3}^{2-} \rightarrow 2 I^{-} + S_{4}O_{6}^{2-}$.