The stability of a complex is measured as stability constant, K‌stability ‌ (A) [AlF6]3−;K‌stability ‌=25×104 (B) [Cd(CN)4]2−;K‌stability ‌=1.7×1016 (C) [Ag(CN)2]−;K‌stability ‌=6.6×1018 (D) [Zn(CN)2]2−;K‌stability ‌=1.0×1018 Thus, the increasing order of stability A<B<D<C