Which metal sulphide is soluble in excess $NH_3$ solution?

The hydrolysis constants of salts $NaA$ and $NaB$ (of weak acids $HA$ and $HB$) are $10^{-8}$ and $10^{-10}$ respectively. If the dissociation constant of weak acid $HC$ is $10^{-5}$,what is the decreasing order of acidic strength?

Which of the following statement$(s)$ is/are correct?
$ (A) $ The $pH$ of $1 \times 10^{-8} \ M \ HCl$ solution is $8$.
$ (B) $ The conjugate base of $H_2PO_4^{-}$ is $HPO_4^{2-}$.
$ (C) $ $K_w$ increases with increase in temperature.
$ (D) $ When a solution of weak monoprotic acid is titrated against a strong base at half neutralisation point,$pH = pK_a$.
Choose the correct answer from the option given below.

During the titration of acetic acid with an aqueous $NaOH$ solution,the neutralization graph shows a vertical line. This line indicates:

On decreasing the $pH$ from $7$ to $2$,the solubility of a sparingly soluble salt $(MX)$ of a weak acid $(HX)$ increased from $10^{-4} \ mol \ L^{-1}$ to $10^{-3} \ mol \ L^{-1}$. The $pK_{a}$ of $HX$ is:

The dissociation of water at $25 \, ^\circ C$ is $1.9 \times 10^{-7} \%$ and the density of water is $1.0 \, g/cm^3$. The ionisation constant of water is