An acid type indicator HIn differs in colour from its conjugate base (`In^(-))`. The human eye is sensitive to colour differences only when the ratio `(In^(-))`/[Hin) is greater than 10 or smaller than 0.1. What should be the minimum change in the pH of the solution to observe a complete colour change `(K_(a) = 1.0 xx 10^(-5))` ? : 3, 4, 1, 2

Options

A. 3
B. 4
C. 1
D. 2

Answer

D

Explanation

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