Which one of the following metal salts produces a blue coloured bead in cobalt nitrate charcoal cavity test ?

Options

A. `Zn^(2+)`
B. `Mg^(2+)`
C. `Sn^(2+)`
D. `Al^(3+)`

Answer

D

Explanation

`Al_(2)O_(3). CoO` formed in the test is blue in colour. It is called as thenard's blue.