The coloured ions give characteristics colour beads in the borax bead test due to formation of:

The coloured ions give characteristics of colour beads in the borax bead test due to the formation of metal metaborates.

 The qualitative inorganic analysis uses the borax bead test to detect the presence of certain metals. A lower reducing flame is used to heat the coated bead at first, followed by a stronger oxidising flame. Most often, the formation of metal metaborates salts of chromium, copper, or nickelcauses distinctive colours.

 The following reaction for metaborate we obtained,

${\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7+{\mathrm{CuSO}}_4\to 2{\mathrm{NaBO}}_2+\underset{\text{ Copper metaborate.(blue) }}{\mathrm{Cu}{\left({\mathrm{BO}}_2\right)}_2}+{\mathrm{SO}}_3$

Hence, option B is correct.