A $1\mathrm{.}00-$L solution contains $4\mathrm{.}00{10}^{-4}$MCu$(N{O}_3{)}_2$ and $2\mathrm{.}40{10}^{-3}M$ ethylenediamine $($en$).$ The $K_f$ for $Cu(en{)}_2^{2+}$ is $1\mathrm{.}00{10}^{20}$

$C{u}^{2+}(aq)+2en(aq)Cu(en{)}_2^{2+}(aq)$

$K_f=\frac{[Cu(en{)}_2^{2+}]}{[C{u}^{2+}][en{]}^2}$

$4$th attempt

See Hint

What is the concentration of $C{u}^{2+}(aq)$ in the solution?