An acid indicator is represented by `Hl_(n).(K_(a)=10^(-5))`. The range of change of colour for the indicator is

Options

A. `3-5`
B. `4-6`
C. `5-7`
D. `6-8`

Answer

2

Explanation

For indicator equilibrium
`HI_(a)hArr H^(+)(aq)+ln(aq)`
`K_(Hln)=([H^(+)][ln^(-)])/([Hln])" "or" "[H^(+)]=K_(Hln)([Hln])/([ln^(-)])`
`log[H^(+)]=logK_(Hln)+log.([Hln])/([ln^(-)])rArr" "pH=pK_(Hln)+log.([ln^(-)])/([Hln])`
If colour of `ln^(-)` is to be observed `,[ln^(-)]ge10[Hln^(-)]" "or" "pH=pK_(Hln)+1`
If colour of `[Hln^(-)]` is to be observed `,10[Hln^(-)]ge[ln^(-)]" "or " "pH=pK_(Hln)+-1`
Heere `(4)` Ans.