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

The amount of oxalic acid in a solution can be determined by titration with $KMnO_4$ in the presence of $H_2SO_4$. If the titration is performed in the presence of $HCl$,the results are unsatisfactory because $HCl$ ...

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 $M$)

The strength of an aqueous $NaOH$ solution is most accurately determined by titrating it against a standard solution of oxalic acid. (Note: consider that an appropriate indicator is used)

When $10 \ mL$ of an aqueous solution of $Fe^{2+}$ ions was titrated in the presence of dil $H_{2}SO_{4}$ using diphenylamine indicator,$15 \ mL$ of $0.02 \ M$ solution of $K_{2}Cr_{2}O_{7}$ was required to get the end point. The molarity of the solution containing $Fe^{2+}$ ions is $X \times 10^{-2} \ M$. The value of $x$ is $....$ (Nearest integer)

What is the indicator used in Argentometric titrations?