Urea reacts with water to form A, which will decompose to form B. B when passed through ${\mathrm{Cu}}^{2+}$(aq), deep blue colour solution C is formed. What is formula of C from the following?  

${\text{NH}}_{\text{2}}{\text{CONH}}_{\text{2}}\stackrel{{\text{H}}_{\text{2}}\text{O}/∆,}{\to }{\text{NH}}_{\text{3}}\stackrel{{\text{Cu}}_{\text{(aq)}}^{\text{2+}}}{\to }{{\text{[Cu(NH}}_{\text{3}}{\text{)}}_{\text{4}}\text{]}}^{\text{2+}}$

                                                                            deep blue 
                                                                       colour solution