The pairs of compounds which cannot exist together in aqueous solution are :
$I. NaH_2PO_4$ and $Na_2CO_3$ $II. Na_2CO_3$ and $NaHCO_3$
$III. NaOH$ and $NaH_2PO_4$ $IV. NaHCO_3$ and $NaOH$

Which $pH$ value is higher in the following pairs?
$(a)$ $0.1 \ M \ HCl$ and $0.1 \ M \ NaOH$
$(b)$ $0.1 \ M \ HCl$ and $0.01 \ M \ HCl$
$(c)$ $0.1 \ M \ NaOH$ and $0.01 \ M \ NaOH$

What would happen when a solution of potassium chromate is treated with an excess of dilute nitric acid?

$A$ certain amount of $H_2CO_3$ and $HCl$ are dissolved to form $1 \ L$ solution. At equilibrium,it is found that the concentrations of $H_2CO_3$ and $CO_3^{2-}$ are $0.1 \ M$ and $0.01 \ M$ respectively. Calculate the $pH$ of the solution. Given that for $H_2CO_3$,$K_{a_1} = 10^{-5}$ and $K_{a_2} = 10^{-8}$.

In a saturated solution of $Mg(OH)_2$,the degree of dissociation of $Mg(OH)_2$ is $\alpha$. Find the concentration $(C)$ of $Mg(OH)_2$ if the concentration of $[OH^{-}]$ is $2$.

When $NaCl$ is dissolved in water,the sodium ion is