A borax sample is investigated. Which statements are correct?

AWith a copper(II) salt in the oxidising flame, the cold bead is blue
BHeated with ethanol and conc. $H X_{2} SO X_{4}$ , its vapour burns with a red flame
COn strong heating it swells and then fuses to a glassy bead containing $NaBO X_{2}$ and $B X_{2} O X_{3}$
DIts aqueous solution is alkaline because $Na X_{2} B X_{4} O X_{7} + 7 H X_{2} O 2 NaOH + 4 H X_{3} BO X_{3}$ and the weak acid leaves the strong base in solution

Answer: A, C, D

Borax is the salt of a strong base and a weak acid, so hydrolysis gives an alkaline solution. Heating removes water of crystallisation and gives

NaBO X_{2}

and

B X_{2} O X_{3}

as a glassy bead, which dissolves metal oxides to give coloured metaborates (

Cu (BO X_{2}) X_{2}

, blue when cold). The ethyl borate flame is green-edged, not red.