Which of the following arrangement shows the correct order of increasing stability ?

Question

$(a)\;N^{2+} < AS^{2+} < Sb^{2+} < Bi^{2+} \\(b)\;Zn^{2+} < Cu^{2+} < AS^{2+} < Bi^{2+} \\ (c)\;Cu^{2+} < CO^{2+} < P^{2+} < N^{2+} \\ (d)\;C^{2+} < Ge^{2+} < Sn^{2+} < Pb^{2+}$