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# $pH$ at which an acidic indicator with $K_{in} = 1 \times 10^{-5}$ changes colour when the indicator is $1 \times 10^{-3}$ M is

(a) 8

(b) 4

(c) 3

(d) 5

The $pH$ at which an acidic indicator changes colour is equal to its $pK_{in}$ and is independent of its concentration
$pH = pK_{in} (acidic) = - log 10^{-5} = 5$