Why are strong acids generally used as standard solutions in acid-base titrations?

In the titration of a strong acid and a weak base,the indicator used is:

In an acid-base titration,$0.1 \ M \ HCl$ solution was added to the $NaOH$ solution of unknown strength. Which of the following correctly shows the change of $pH$ of the titration mixture in this experiment?

$20 \ mL$ of $HCl$ solution requires $19.85 \ mL$ of $0.01 \ M$ $NaOH$ solution for complete neutralization. The molarity of $HCl$ solution is

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

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: