What is the indicator used in Argentometric titrations?

For standardizing $NaOH$ solution,which of the following is used as a primary standard?

$0.4 \ g$ mixture of $NaOH, Na_{2}CO_{3}$ and some inert impurities was first titrated with $\frac{N}{10} \ HCl$ using phenolphthalein as an indicator,$17.5 \ mL$ of $HCl$ was required at the end point. After this,methyl orange was added and titrated. $1.5 \ mL$ of same $HCl$ was required for the next end point. The weight percentage of $Na_{2}CO_{3}$ in the mixture is .......... (Rounded-off to the nearest integer)

Which of the following titrations is methyl orange the best indicator for?

If $25 \ mL$ of $H_2SO_4$ solution is neutralized by $32.63 \ mL$ of $0.164 \ M \ NaOH$ solution,what is the molarity of the $H_2SO_4$ solution?

$300 \ mL$ 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 $V = ....... \ mL$