In an acidic medium, $10 mL$ of $0.25 M$ oxalic acid is titrated with $KMnO_4$ solution. If the volume of $KMnO_4$ solution required to reach the end point is $10 mL$, the strength of the $KMnO_4$ solution is (in $M$)

$0.4 \ g$ 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)

Phenolphthalein is used as an indicator for the titration of sodium hydroxide solution against a standard solution of oxalic acid. The colour change that is observed at an alkaline pH close to the equivalence point during this titration is:

$3.92 \, g$ of ferrous ammonium sulphate crystals are dissolved in $100 \, mL$ of water. $20 \, mL$ of this solution requires $18 \, mL$ of $KMnO_4$ during titration for complete oxidation. The weight of $KMnO_4$ present in one litre of the solution is ............. $g$.

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

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