Answer: D. Test the cation \(\text{Zn}^{2+}\) and the anion \(\text{SO}_4^{2-}\).
Cation: with aqueous NaOH, \(\text{Zn}^{2+}\) gives a white precipitate of \(\text{Zn(OH)}_2\) which dissolves in excess NaOH (forming the soluble zincate). The same happens with aqueous \(\text{NH}_3\). The key word is 'dissolves'.
Anion: sulfate is identified by adding aqueous barium nitrate \(\text{Ba(NO}_3)_2\) in acidic conditions (dilute \(\text{HNO}_3\) prevents carbonate or sulfite false positives). A white precipitate of barium sulfate \(\text{BaSO}_4\) confirms sulfate is present.
Row D matches: NaOH dissolves the precipitate (correct cation behaviour) and aqueous barium nitrate gives the white precipitate (correct anion test). Aqueous sodium nitrate (in C) is meaningless as an anion test.
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