Following are some of the certain facts of Ostwald's theory of $$acid-base$$ indicators.I : Ionised and unionised forms have different colours.II : Colour change is indicated at the end point when unionised form changes to ionised form due to change in pH.III : Benzenoid form changes to quinonoid form and $$vice-versa$$ due to change in PH.Select the correct facts

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Ostwald's theory: According to this theory:(a) The colour change is due to ionisation of the $$acid-base$$ indicator. The unionised form has different colour than the ionised form.(b) The ionisation of the indicator is largely affected in acids and bases as it is either a weak acid or a weak base. In case, the indicator is a weak acid, its ionisation is very much low in acids due to common $$H+$$ ions while it is fairly ionised in alkalies. Similarly if the indicator is a weak base, its ionisation is large in acids and low in alkalies due tocommon $$OH-$$ ions.

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