$10.0 \, mL$ of $Na_{2}CO_{3}$ solution is titrated against $0.2 \, M \, HCl$ solution. The following titre values were obtained in $5$ readings.
$4.8 \, mL, 4.9 \, mL, 5.0 \, mL, 5.0 \, mL$ and $5.0 \, mL$
Based on these readings,and convention of titrimetric estimation,the concentration of $Na_{2}CO_{3}$ solution is .... $mM$.
(Round off to the nearest integer)

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

Given below are two statements :
Statement $I$ : Potassium hydrogen phthalate is a primary standard for standardisation of sodium hydroxide solution.
Statement $II$ : In this titration,phenolphthalein can be used as an indicator.
In the light of the above statements,choose the most appropriate answer from the options given below:

What is the indicator used in Argentometric titrations?

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:

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 $:$