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 Leftrightarrow H^+ +In^(-)`
`K_a=([H^+] [In^(-)])/[HIn]`
When `([In^(-)])/([HIn])=10, K_(a)=[H^+] xx 10`
`" "[H^+]=1 xx 10^(-5)//10=10^(-6)`
pH =6
When `([In^(-)])/(HIn]=1/(10), [H^+]=1 xx 10^(-5) xx 10=10^(-4)`
minimum change in pH =6-4=2