$25 \ mL$ of a solution of barium hydroxide on titration with a $0.1 \ M$ solution of hydrochloric acid gave a titre value of $35 \ mL$. The molarity of barium hydroxide solution was (in $M$)

In a conductometric titration,a small volume of titrant of higher concentration is added stepwise to a larger volume of titrate of much lower concentration,and the conductance is measured after each addition.
The limiting ionic conductivity ( $\Lambda ^0$ ) values (in $mS \ m ^2 \ mol ^{-1}$ ) for different ions in aqueous solutions are given below:

Ions	$Ag ^{+}$	$K ^{+}$	$Na ^{+}$	$H ^{+}$	$NO _3^{-}$	$Cl ^{-}$	$SO _4^{2-}$	$OH ^{-}$	$CH _3COO ^{-}$
$\Lambda _0$	$6.2$	$7.4$	$5.0$	$35.0$	$7.2$	$7.6$	$16.0$	$19.9$	$4.1$

For different combinations of titrates and titrants given in List-$I$,the graphs of 'conductance' versus 'volume of titrant' are given in List-$II$.

List-$I$	List-$II$
$(P)$ Titrate: $KCl$,Titrant: $AgNO _3$	$(1)$ Graph showing initial decrease then increase
$(Q)$ Titrate: $AgNO _3$,Titrant: $KCl$	$(2)$ Graph showing sharp decrease then sharp increase
$(R)$ Titrate: $NaOH$,Titrant: $HCl$	$(3)$ Graph showing slight decrease then increase
$(S)$ Titrate: $NaOH$,Titrant: $CH _3COOH$	$(4)$ Graph showing continuous increase
	$(5)$ Graph showing decrease then constant

Match each entry in List-$I$ with the appropriate entry in List-$II$ and choose the correct option.

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:

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 $:$

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)

Solution $X$ contains $Na_2CO_3$ and $NaHCO_3$. $20 \ mL$ of $X$ when titrated using methyl orange indicator consumed $60 \ mL$ of $0.1 \ M \ HCl$ solution. In another experiment,$20 \ mL$ of $X$ solution when titrated using phenolphthalein consumed $20 \ mL$ of $0.1 \ M \ HCl$ solution. The concentrations (in $mol \ L^{-1}$) of $Na_2CO_3$ and $NaHCO_3$ in $X$ are respectively: