When borax is heated with CoO on a platinum loop, blue coloured bead formed is largely due to

Step-by-step solution

On heating, borax loses its water of crystallisation and decomposes to give sodium metaborate and boric anhydride Na 2   B 4 O 7 · 10 H 2 O ⟶ Δ Na 2   B 4 O 7 + 10 H 2 O Na 2   B 4 O 7 ⟶ Δ 2 NaBO 2 (sodium meta borate) + B 2 O 3 On treatment with metal salt, boric anhydride forms metaborate of the metal which gives different colours in oxidising and reducing flame. For example, in the case of copper sulphate, following reactions occur B 2 O 3 + CoO → Co BO 2 2 (coba