Which of the following best describes the wavelength of the prominent spectral line emitted by potassium chloride (KCl) when excited in a flame test?

• A. Approximately 656 nm, corresponding to the lithium emission
• B. Approximately 486 nm, corresponding to the hydrogen Balmer series
• C. Approximately 589 nm, corresponding to the sodium emission
• D. Approximately 766 nm, corresponding to the potassium emission

Answer: (D)

Verified step by step guidance

1. Understand that the flame test identifies elements based on the characteristic wavelengths of light they emit when excited by heat.
2. Recall that each element has a unique emission spectrum, with specific prominent lines at certain wavelengths.
3. Recognize that potassium chloride (KCl) contains potassium ions, so the emission lines observed in the flame test correspond to potassium, not lithium, hydrogen, or sodium.
4. Know the approximate wavelength of the prominent potassium emission line is around 766 nm, which is in the red to near-infrared region of the visible spectrum.
5. Compare the given options and match the wavelength to the element's known emission line to confirm that 766 nm corresponds to potassium emission.