A salt imparts a yellow colour to a borax bead in an oxidising flame. What would be the colour of th — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Step 1: This represents a classic thermal color behavior of zinc oxide. Step 2: Upon heating, zinc oxide (ZnO) loses a tiny fraction of oxygen from its crystal lattice, creating non-stoichiometric defects that absorb light in the blue region, turning it yellow. On cooling, the oxygen is re-absorbed or the lattice relaxes, returning it to white. Step 3: Therefore, the residue that is yellow when hot and white when cold is ZnO, indicating the presence of zinc (Zn2+) in the salt, matching option (b).