The stepwise formation of [Cu(NH₃)₄]²⁺ is given below.

In, Cu²⁺+NH₃​⇌K1​​[Cu(NH₃​)]²⁺

= [Cu(NH₃​)]²⁺+NH₃​⇌K₂​​[Cu(NH₃​)₂​]²⁺ 

= [Cu(NH₃​)₂​]²⁺+NH₃​⇌K³​​[Cu(NH₃​)_3​]²⁺ 

= [Cu(NH₃​)₃​]²⁺+NH_3​⇌K⁴​​[Cu(NH₃​)⁴​]²⁺ 

Stability constants values are as follows

K1​,K2​,K3​ and K4​ are 10⁴,1.58×10³,5×10² and 10²

Whereas, K=${\mathrm{K}}_1\times {\mathrm{K}}_2\times {\mathrm{K}}_3\times {\mathrm{K}}_4$; K=$7.9\times {10}^{11}$

$$\begin{gathered} \mathrm{K}\text{'}= \frac{1}{\mathrm{K}} \\ \mathrm{K}\text{'} = \frac{1}{7.9 \times {10}^{11}} \\ = 1.26 \times {10}^{-12} \\ = \mathrm{x} \mathrm{is} 1.26 \end{gathered}$$