Two solutions $A$ and $B$,each of $100 \; L$,were made by dissolving $4 \; g$ of $NaOH$ and $9.8 \; g$ of $H_{2}SO_{4}$ in water,respectively. The $pH$ of the resultant solution obtained by mixing $40 \; L$ of solution $A$ and $10 \; L$ of solution $B$ is:

$A$ solution of $0.1 \ M$ weak base $(B)$ is titrated with $0.1 \ M$ of a strong acid $(HA)$. The variation of $pH$ of the solution with the volume of $HA$ added is shown in the figure below. What is the $pK_{b}$ of the base? The neutralization reaction is given by $B + HA \rightarrow BH^{+} + A^{-}$.

For a weak acid $HCN$ at $25 \, ^\circ C$,which of the following statements is correct?

$1 \times 10^{-5} \ S \ M$ $AgNO_3$ 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 $298 \ K$,$\lambda^0_{Ag^{+}} = 6 \times 10^{-3} \ S \ m^2 \ mol^{-1}$,$\lambda^0_{Br^{-}} = 8 \times 10^{-3} \ S \ m^2 \ mol^{-1}$,$\lambda^0_{NO_3^-} = 7 \times 10^{-3} \ S \ m^2 \ mol^{-1}$.

$A$ sample of $MgCO_3$ is dissolved in dil. $HCl$ and the solution is neutralized with ammonia and buffered with $NH_4Cl / NH_4OH$. Disodium hydrogen phosphate reagent is added to the resulting solution. $A$ white precipitate is formed. What is the formula of the precipitate?

The hydrogen ion concentration of a $0.1 \ N$ solution of $CH_3COOH$,which is $30 \%$ dissociated,is (in $M$)