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

`"HIn" hArr H^(+) + In^(-), K_(a) = ([H^(+)][In^(-)])/(["HIn"]) or [H^(+)] = K_(a) (["HIn"])/([In^(-)])`
When `([In^(-)])/(["HIn"])=10, [H^(+)]=10^(-5)xx(1)/(10) = 10^(-6), pH = 6`
When `([In^(-)])/(["HIn"])=0.1 , [H^(+)]=10^(-5)xx10=10^(-4), pH=4" " :. ` Minimum change in pH = 2