Which of the following cations can be identified using a flame test? (A) Al$^{3+}$ (B) Cu$^{2+}$ (C) Mg$^{2+}$ (D) Zn$^{2+}$ - HSC - SSCE Chemistry - Question 3 - 2004 - Paper 1

The flame test is a qualitative analysis technique used to identify the presence of certain metal ions based on the color of the flame they produce when heated.

• Al$^{3+}$: Aluminum cations do not produce a distinctive color in a flame test, making it difficult to identify this particular ion using this method.
• Cu$^{2+}$: Copper ions, on the other hand, produce a bright green flame, allowing for easy identification.
• Mg$^{2+}$: Magnesium ions do not produce a color detectable in a flame test, similar to aluminum.
• Zn$^{2+}$: Zinc ions also do not impart any significant color in a flame test.

Based on this information, the only cation that can be identified using a flame test from the options provided is Cu$^{2+}$ (Option B).