`50 ml, 0.1M NaHCO_(3)` aqueous solution is mixed with `50 ml, 0.8 M Na_(2)CO_(3)` aqueous solution at `25^(@)C`. The `pH` of resulting solution exiists between colour transition range of an indicator which is:
`(K_(a_(1))=4xx10^(-7), K_(a_(2)) =2xx10^(-11) "for" H_(2)CO_(3))`

Options

A. Phenol red `(6.8 "to" 8.4)`
B. Propyl red `(4.6 "to" 6.4)`
C. Phenolphathalein `(8.3 "to" 10.1)`
D. Malachite green `(11.4 "to" 13)`

Answer

D

Explanation

Buffer solution
`pH=pK_(a_(2))+log[CO_(3)^(-2)]/([HCO_(3)^(-)])=(11-log2)+log((40)/(5))`
`=11+21log2 = 11.6`