What will be the change in acidity if
$(i)$ $CuSO_4$ is added in saturated $(NH_4)_2SO_4$ solution
$(ii)$ $SbF_5$ is added in anhydrous $HF$?

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

$1 \times 10^{-5} \ S \ M$ $AgNO_3$ is added to $1 \ L$ of a saturated solution of $AgBr$. The conductivity of this solution at $298 \ K$ is $......... \times 10^{-8} \ S \ m^{-1}$.
Given: $K_{sp}(AgBr) = 4.9 \times 10^{-13}$ at $298 \ K$,$\lambda^0_{Ag^{+}} = 6 \times 10^{-3} \ S \ m^2 \ mol^{-1}$,$\lambda^0_{Br^{-}} = 8 \times 10^{-3} \ S \ m^2 \ mol^{-1}$,$\lambda^0_{NO_3^-} = 7 \times 10^{-3} \ S \ m^2 \ mol^{-1}$.

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

What is the concentration of $[OH^-]$ in a mixture of $20 \ mL$ of $0.050 \ M \ HCl$ and $30 \ mL$ of $0.10 \ M \ Ba(OH)_2$ (in $M$)?

In which case is the change in $pH$ maximum?