The overall stability constant of the complex ion ${\left[\mathrm{Cu}{\left({\mathrm{NH}}_3\right)}_4\right]}^{2+}$ is 2.1 $\times {10}^{13}$. The over all dissociation constant is $\mathrm{y}\times {10}^{-14}$. If y is an integer it is equal to

The complex ion's overall stability constant ${\left[\mathrm{Cu}{\left({\mathrm{NH}}_3\right)}_4\right]}^{2+}$ is 2.1 $\times {10}^{13}$. Overall, the dissociation constant is $\mathrm{y}\times {10}^{-14}$. If y is an integer, it equals to 5.

Given ${\mathrm{k}}_{\mathrm{f}}=2.1\times {10}^{13}$
${\mathrm{K}}_{\mathrm{d}}=\frac{1}{{\mathrm{k}}_{\mathrm{f}}}=4.7\times {10}^{-14}$$\therefore y=4.7=5$

Hence, the required answer is 5.