Directions : In the following question more than one of the answers given may be correct. Select the correct answer and mark it according to the code:
Which of the following statement(s) is (are) correct? (1)\[HPO_{4}^{2-}\]is the conjugate base of\[{{H}_{2}}PO_{4}^{-}\] (2) The pH of\[1.0\times {{10}^{-8}}M\]solution of\[HCl\]is 8 (3) Autoprotolysis constant of water increases with temperature (4) When a solution of a weak monoprotic acid is treated against a strong base, at half-neutralisation point,\[pH=\frac{1}{2}p{{K}_{a}}\]A) 1, 2 and 3 are correct
B) 1 and 2 are correct
C) 2 and 4 are correct
D) 1 and 3 are correct
Correct Answer: D
Solution :
(1) \[{{H}_{2}}PO_{4}^{2-}\xrightarrow[{}]{-{{H}^{+}}}\underset{conjugate\,base}{\mathop{HPO_{4}^{2-}}}\,\] (2) \[pH\]of\[1\times {{10}^{-8}}M\,HCl\approx 6.8\] (3) Autoprotolysis constant of water increases with temperature. (4) At half-neutralisation point, \[[{{X}^{-}}]=[HX]\] \[\therefore \] \[pH=p{{K}_{a}}\]
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