$8 \ mL$ of $\frac{N}{10} \ HCl$ are required to neutralize $20 \ mL$ of $Na_2CO_3$ solution in water. The normality of the $Na_2CO_3$ solution is: (in $N$)

Given below are two statements:
Statement $I$: In the oxalic acid vs $KMnO_4$ (in the presence of dil. $H_2SO_4$) titration,the solution needs to be heated initially to $60^{\circ}C$,but no heating is required in Ferrous Ammonium Sulphate $(\text{FAS})$ vs $KMnO_4$ titration (in the presence of dil. $H_2SO_4$).
Statement $II$: In oxalic acid vs $KMnO_4$ titration,the initial formation of $MnSO_4$ takes place at high temperature,which then acts as a catalyst for the further reaction. In the case of $\text{FAS}$ vs $KMnO_4$,heating oxidizes $Fe^{2+}$ into $Fe^{3+}$ by oxygen of air and error may be introduced in the experiment.
In the light of the above statements,choose the correct answer from the options given below:

$20 \ mL$ of $HCl$ solution requires $19.85 \ mL$ of $0.01 \ M$ $NaOH$ solution for complete neutralization. The molarity of $HCl$ solution is

$50 \ cm^{3}$ of $0.2 \ N \ HCl$ is titrated against $0.1 \ N \ NaOH$ solution. The titration was discontinued after adding $50 \ cm^{3}$ of $NaOH$. The remaining titration is completed by adding $0.5 \ N \ KOH$. The volume of $KOH$ required for completing the titration is (in $cm^{3}$)

Which of the following reactions occurs during iodometric titration in the laboratory?

Which reagent is commonly used for the determination of water hardness by titration?