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Which of the following statement(s) is/are correct ? (A) The pH of 1 × 10^-8 M HCl solution is 8 (B) The conjugate base of H2PO4^- is HPO4^2- (C) K_w increases with increase in temperature (D) When a solution of a weak monoprotic acid is titrated against a strong base at half neutralisation point, pH = 1/2 pK_a Choose the correct answer from the options given below :

1. (1) (B), (C)
2. (2) (A), (D)
3. (3) (A), (B), (C)
4. (4) (B), (C), (D)

Correct answer: (1) (B), (C)

Solution

Option (B) is correct because HPO4^2- is indeed the conjugate base of H2PO4^-. Option (C) is also correct as the ion product of water, K_w, increases with temperature due to the endothermic nature of water dissociation. Option (A) is incorrect because the pH of a 1 × 10^-8 M HCl solution is not 8, and option (D) is incorrect as the pH at the half-neutralization point is equal to pK_a, not 1/2 pK_a.

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