Which flame color indicates the presence of lithium ions?

• A. Red
• B. Yellow
• C. Blue
• D. Green

Answer: (A)

Flame tests work because heating metal ions excites their electrons, and when those electrons fall back to lower energy levels they emit light at specific wavelengths. For lithium ions, the emitted light falls in the red part of the spectrum, so the flame looks red (often described as crimson). This red flame is the telltale sign of lithium. Other metals produce different flame colors—sodium gives a bright yellow, potassium a lilac, copper a blue‑green—so seeing red points to lithium. In practice, sodium’s strong yellow light can mask lithium’s red, so it's best to use a clean sample or a spectroscope to confirm.