In the volumetric analysis of $HCl$,if we use phenolphthalein as an indicator,which base is unsuitable for titration?

While titrating a dilute $HCl$ solution with an aqueous $NaOH$ solution,which of the following will not be required?

If soap has a high alkali content,it irritates the skin. How can the amount of excess alkali be determined? What can be the source of excess alkali?

$25 \ mL$ 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 $M$)

The indicator used during the estimation of $COD$ of a water sample is

$8 \ mL$ 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 $N$)