An aqueous solution of an unknown inorganic salt is treated with solid NH ₄ Cl and an aqueous solution of NH ₄ OH . Upon subsequent addition of an aqueous solution of ( NH ₄)₂ CO ₃ , a white precipitate is formed. Which of the following cations is most likely present in the solution?

Step-by-step solution

The reagent mixture of NH ₄ Cl , NH ₄ OH , and ( NH ₄)₂ CO ₃ is the group reagent for Group V cations in systematic qualitative analysis. The Group V cations include Ba ²⁺ , Sr ²⁺ , and Ca ²⁺ . They precipitate as their respective insoluble carbonates (e.g., SrCO ₃ ). Mg ²⁺ belongs to Group VI and does not precipitate here because the presence of NH ₄ Cl suppresses the ionization of ( NH ₄)₂ CO ₃ , keeping the carbonate ion concentration too low to exceed the solubility product of MgCO ₃ . Zn ²⁺ (Group IV) and Cu ²