In the titration of $Na_2CO_3$ with $HCl$ using phenolphthalein as an indicator,what will be the result?

During the estimation of oxalic acid $V/S$ $KMnO_4$,the self-indicator is:

In the titration of potassium permanganate $(KMnO_4)$ against ferrous ammonium sulphate $(FAS)$ solution,dilute sulphuric acid $(H_2SO_4)$ but not nitric acid $(HNO_3)$ is used to maintain an acidic medium,because:

$300 \ mL$ of deci-molar solution of $Ba(OH)_{2(aq)}$ was titrated with $100 \ mL$ of $0.2 \ M \ HCl_{(aq)}$ solution. The final solution had to be titrated with $V \ mL$ of semi-molar $H_2SO_{4(aq)}$ solution for end-point. Correct option is $V = ....... \ mL$

Temporary hardness in tap water is measured in terms of parts of $CaCO_3$ per $10^6$ parts of water. If $500 \ mL$ of hard water containing $Ca(HCO_3)_2$ was titrated against $\frac{1}{20} \ M \ H_2SO_4$ solution in the presence of a methyl orange indicator,and it required $40 \ mL$ of titrant,then the temporary hardness in the tap water is .............. $ppm$.

$40 \ mL$ of a mixture of $CH_3COOH$ and $HCl$ (aqueous solution) is titrated against $0.1 \ M$ $NaOH$ solution conductometrically. Which of the following statements is correct?