Chemistry

Problem

Which of the following pairs of cations cannot be separated by adding

NH_4Cl

and

NH_4OH

to the mixture and then passing

H_2S

through it? a.

Co^{2+}

Ca^{2+}

Ni^{2+}

Sr^{2+}

Co^{2+}

Ni^{2+}

Zn^{2+}

Ba^{2+}