In the titration of $I_{2(aq)}$ by $S_2O_3^{2-}{_{\text{(aq)}}}$ using the starch indicator,the end point is indicated by:

In the volumetric analysis of $HCl$,if we use phenolphthalein as an indicator,which base is unsuitable for titration?

The indicator used during the estimation of $COD$ of a water sample is

$0.4 \ g$ mixture of $NaOH, Na_{2}CO_{3}$ and some inert impurities was first titrated with $\frac{N}{10} \ HCl$ using phenolphthalein as an indicator,$17.5 \ mL$ of $HCl$ was required at the end point. After this,methyl orange was added and titrated. $1.5 \ mL$ of same $HCl$ was required for the next end point. The weight percentage of $Na_{2}CO_{3}$ in the mixture is .......... (Rounded-off to the nearest integer)

Which of the following statements is correct?

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