Which test is used to identify metal cations by the color produced in a flame?

• A. Chromatography
• B. Titration
• C. Precipitation
• D. Flame test

Answer: (D)

When metal ions are heated in a flame, their electrons get excited and then fall back to lower energy levels, releasing light at specific wavelengths. Those wavelengths appear as characteristic flame colors for different metals, so you can identify which metal cation is present by the observed color.

In practice, you dip a clean wire into the sample and place it in a blue flame, watching for the distinctive color. For example, some common emissions are bright yellow from sodium, crimson from lithium, lilac from potassium, brick-red from calcium, and green or blue-green from copper. Sodium can dominate the flame, so techniques to minimize that interference are sometimes used.

Other tests mentioned, like chromatography, titration, or precipitation, identify or quantify substances in different ways and do not rely on flame color to identify metal cations. The flame test is the method that uses the flame color to identify metal ions.