JEE Main · 2024 · 30 Jan 2024 · Shift 2 · s-Block Elements

A flame test works because the flame's heat promotes an outer electron of a metal ion to a higher energy level, and light of a characteristic wavelength is emitted as the electron falls back — this requires a low-lying, thermally accessible excited state, typical of s-block and a few p-block ions. ${\text{Sr}}^{2+}$ (crimson red), ${\text{Ba}}^{2+}$ (apple green), ${\text{Ca}}^{2+}$ (brick red) and ${\text{Cu}}^{2+}$ (blue-green) each give a distinct flame colour. The first-row transition ions ${\text{Zn}}^{2+}$, ${\text{Co}}^{2+}$ and ${\text{Fe}}^{2+}$ do not give a characteristic flame colour under the standard test. Four of the seven metal ions are characterised by the flame test.