Borax `[Na_(2)B_(4)O_(7).10H_(2)O]` when heated on platinum loop it gives a dark transparent glass like bead. The hot bead is dipped in the salt till it reacts with transition metal oxide. It produces characteristic bead of meta borate.
`{:(" Colour of the bead"," lon"),("(a) Blue green or light blue",Cu^(+2)),("(b) Yellow",Fe^(+2)or Fe^(+3)),("(c) Green",Cr^(+3)),("(d) Violet",Mn^(+2)),("(e) Dark blue",Co^(+2)),("(f) Brown",Ni^(+2)):}`
Glassy bead is of
A. `B_(2)O_(3)+NaBO_(2)`
B. `Na_(3)BO_(3)`
C. `Na_(2)B_(4)O_(7)`
D. `SiO_(2)`
