The colour developed for Co²⁺ basic radical in borax bead test is

detailed solution

Correct option is D

When small amount of Borax is taken in pt loop and heated strongly then it turned to "Transparent glassy bead" (TPGB).For this transparent glassy bead add small quantity of unknown transition metal salt and heated again.Then it gives specified colour to the transparent glassy bead.The colour is due to the formation of respective transition metal meta borate.Based on the colour of TPGB we can detect the transition metal present in the unknown transition metal salt.This test is used to detect the transition metal present in the salt qualitatively.Hint: GPGB3