On performing a borax-bead test with a given inorganic mixture for qualitative analysis,the colour of the bead was found to be emerald green both in oxidising and reducing flame. It indicates the possibility of the presence of

What is microcosmic salt?

When sodium chloride is heated with concentrated $H_2SO_4$ and solid potassium dichromate,which compound containing $Cr$ in the $+6$ oxidation state is formed as a gas?

Which one of the following metals will give blue ash when its salt is heated with $Na_2CO_3$ solid and $Co(NO_3)_2$ on a charcoal piece?

Identify the last step in wet chemical synthesis of nanomaterial.

Given below are two statements:
Statement $I$: Colourless cupric metaborate is reduced to cuprous metaborate in a luminous flame.
Statement $II$: Cuprous metaborate is obtained by heating boric anhydride and copper sulphate in a non-luminous flame.
In the light of the above statements,choose the most appropriate answer from the options given below.