During the neutralisation of an acid by a base, the end point refers to the completion of reaction. The detection of end point in acid-base neutralisation is usually made by an acid-base indicator. An acid-base indicator is itself a weak acid (Phenolphthalein) or a weak base (Methyl orange). At `50%` ionisation which depends on the medium. the anion furnished by an indicator (acid) cation furnished colour to solution at end point. For example, phenolphthalein dissociation
`underset("Colourless")(HIn)toH^(+)+underset("Pink")(In^(-)),K_(HIn)=([H^(+)][In^(-)])/([HIn])`
is favoured in presence of alkali and pink colour of phenolphthalein ion is noticed as soon as the medium changes to alkali nature. The end point of acid-base neutralisation not necessarily coincides with eqivalence point but it is closer to equivalence point. Also at equivalence point of acid-base neutralisation, pH is not necessarily equal to 7.
Bromophenol blue is an acid having dissociation constant `5.48xx10^(-5)`. The percentage of coloured ion furnished at a ph of 4.84 is :

Options

A. `80%`
B. `40%`
C. `20%`
D. `90%`

Answer

a