An acid type indicator, H In differs in colour from its conjugate base `(In^(-))` . The human eye is sensitive to colour differences only when the ratio `[In^(-)]//[H In]` is greater than 10 or smaller than `0.1`. What should to observe a complete colour change ? `(K_(a)= 1.0xx10^(-5))`

Explanation

The two conditions when colour of indicator will be visible are derived by:
`pH=pK_(a)+log([In^(-)])/([H In])`
(i) `pH=5+log 10=6`
(ii) `pH=5+log 0.1=4`
Thus, minimum change in `pH = 2`