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))`

Answer

B

Explanation

An acid-type indicator "Hin" differs in colour from its conjugate base `("In"^(Theta))`.
`"Hin" hArr H^(o+) + "Ind"^(Theta)`
`pH = pK_(a) +"log" (["Ind"^(Theta)])/(["HIn"])`
i. `pH_(1) = 5+"log"(10)/(1) = 6`
ii. `pH_(2) = 5+ "log" (1)/(10) = 4`
Thus minimum change in `pH` change `=6 -4 = 2`.