Acid base indicators are either weak organic acids or weak organic bases. Indicator change colour in dilute solution when the hydronium ion concentration reaches a particular value. For example, phenopthalein is a colour less substance in any aqueous solution with a pH less than `8.3` in between the pH range `8.3` to `10`, transaction of colour (colourless to pink) takes place and if pH of solution is greater than `10`, then solution colour is dark pin. Considering an acid indicator HIn, base `In^(-)` can be represented as :
`HIn hArr H^(+) + In^(-)`
acidic form basic form pH of solution can be computed as :
`pH = pK_(In) + "log" ([In^(-)])/([HIn])`
In general, transition of colour takes place in between the pH range `pK_(In) +-1`
Select the correct statement among the following

Options

A. In the complete ionisation of indicator its `pH = pK_(In)`
B. Methyl orange (working range : `3.1` to `4.4`) is a suitable indicator for weak acid and strong base
C. Bromothymol blue (working range of `6.0` to `7.6`) is a good indicator for titration of `HCl` and `NaOH`
D. Thymal blue (working range `1.2` to `2.8` ) is good indicator for titration of `100 ml` of `0.1 M NH_(4)OH(pK_(b) = 4.74)` and `0.1 M HCl`.

Answer

C