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JEE Main levelOne or more correct optionsDifficulty 2 of 3ie016

Pure water is heated from 298 K to 373 K, where $K_{w}$ is about $5.5 \times 1 0^{- 13}$ . Which statements are correct?

AThe pH of water falls below 7 but water remains neutral.
B $[H X^{+}] > [OH X^{-}]$ , so water becomes acidic.
C $p K_{w}$ becomes smaller than 14.
DThe autoionisation of water is endothermic.

Answer: A, C, D

Heating raises

K_{w}

(autoionisation absorbs heat), so

p K_{w} < 14

and neutral pH

= p K_{w} /2 < 7

. Still

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

, so water stays neutral; options 1, 3 and 4 are correct.

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