Question

Assertion: pH of water increases with an increase in temperature
Reason: $K_W$ of water increases with increase in temperature

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct
• E. Both Assertion and Reason are incorrect

Answer 1

The correct option is D Assertion is incorrect but Reason is correct

On heating water $K_w$ increases and thus $pH$ scale for neutrality changes from $7$ to some lower value.
(A) is wrong. Dissociation of water is an endothermic reaction so increasing T will increase $\left[H^{\oplus }\right]$ and hence decrease in pH.