Concentration of the $A{g}^{+}$ ions in a saturated solution of $A{g}_{2}C{O}_2{O}_4$ is $2.2\times {10}^{-4}mol{L}^{-1}$ Solubility product of $A{g}_2{C}_2{O}_4$ is:

Key concept - For a sparingly soluble salt, if S is the molar solubility,
$A_x{B}_y\left(s\right)+H_{2}O\iff x{A}^{y+}+y{B}^{x-}$
At saturation,
$K\left[A_x{B}_y\right]={\left[A^{y+}\right]}^x\times {\left[B^{x-}\right]}^y={\left[xS\right]}^x{\left[yS\right]}^y$
or $K_{sp}=x^t.y^y{S}^{x+y}$
Where, the constant $K_{sp}$ is called solubility product.
$A{g}_2{C}_2{O}_4\left(s\right)\iff \underset{2S}{2A{g}^{+}}+\underset{S}{C_2{O}_4^{2-}}$
$K_{sp}={\left[A{g}^{+}\right]}^2\left[C_2{O}_4^{2-}\right]={\left[2S\right]}^2\left[S\right]$
Given, $2S=22\times {10}^{-4}$ or $S=1.1\times {10}^{-4}M$
$\therefore K_{sp}={\left[2.2\times {10}^{-4}\right]}^2\left[1.1\times {10}^{-4}\right]$
$=5.3\times {10}^{-12}$