Al salts on heating with ${\mathrm{Na}}_2{\mathrm{CO}}_3$ in , charcoal cavity gives a white infusible residue. On moistening the same with a drop of cobalt nitrate, it changes to due to the formation of cobalt meta-aluminate (Thenard's blue)

• A

  Brown

• B

  Yellow

• C

  Blue

• D

  Lemon