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`
Which of the following indicator is most suitable for titration of HBr with strong base:

Options

A. Phenolphthalein `(8.3 - 10)`
B. Bromothymol blue `(6-7.6)`
C. Methyl red `(4.2-6.3)`
D. Malachite green `(11.4-13)`

Answer

A