Starch can be used as an indicator for the detection of traces of

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Phenolphthalein is a $pH$ dependent indicator,remains colourless in acidic solution and gives pink colour in basic medium.
Reason $R$: Phenolphthalein is a weak acid. It doesn't dissociate in basic medium.
In the light of the above statements,choose the most appropriate answer from the options given below.

Which indicator is most suitable for the titration of $0.1 \, N \, Na_2CO_3$ solution with $0.1 \, N \, HCl$?

For an acid indicator with $K_{in} = 1.0 \times 10^{-5}$, the color change occurs when the concentration of the indicator is $1 \times 10^{-3} \ M$. Find the $pH$ at which the color change occurs.

If a very small amount of $HPh$ (phenolphthalein) is added to a $0.1 \ M$ aqueous solution of $CH_3COONa$,the fraction of the indicator that exists in the colourless form is:
$[K_b(CH_3COO^{-}) = 10^{-9}, pK_a(HPh) = 9.6, \log 2 = 0.3]$

The indicator used in the titration of $Na_2CO_3$ with $HCl$ is..................