The first and second dissociation constants of an acid ${\mathrm{H}}_2\mathrm{A}$ are $1.0\times {10}^{-5}$ and $5.0\times {10}^{-10}$respectively. The overall dissociation constant of the acid will be: 

$\mathrm{Assertion}:$ When small amount of acid or base is added to pure water, its $\mathrm{pH}$ undergoes a change.

$\mathrm{Reason}:$ Addition of an acid or base increases the degree of ionisation of water.

$\mathrm{Assertion}:$Solubility of $\mathrm{AgBr}$ decreases in the presence of sodium bromide.

$\mathrm{Reason}:$Sodium bromide undergoes hydrolysis in water.

$\mathrm{Assertion}:$ If ${\mathrm{K}}_{\mathrm{sp}}<$ ionic product, precipitate is formed.

$\mathrm{Reason}:$Solubility product $\left({\mathrm{K}}_{\mathrm{sp}}\right)$ is the highest limit of ionic product of the electrolyte in saturated solutions.

Assertion: When an acid or a base is added to water at constant temperature the $\mathrm{pH}$ changes.

Reason: This is due to change in ionic product of water.