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JEE Advanced levelSingle correct optionDifficulty 3 of 3ie036

At a certain temperature $K_{w} = 4.0 \times 1 0^{- 14}$ ( $lo g 2 = 0.301$ ). A solution at this temperature has pH $6.9$ . The solution is

Aacidic
Bneutral
Cneutral, because its pH is close to 7
Dbasic

Answer: D

p K_{w} = 14 - 0.602 = 13.398

, so neutral pH

= 6.699 \approx 6.70

. A pH of

6.9 > 6.70

means

[H X^{+}] < [OH X^{-}]

and the solution is basic, even though pH is below 7.

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