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NEET levelSingle correct optionDifficulty 1 of 3qa114

A borax bead is made with a trace of a copper(II) salt and heated in the oxidising (outer) flame. The colour of the bead after it has cooled is:

Agreen
Bblue
Cviolet
Dcolourless

Answer: B

In the oxidising flame copper(II) metaborate,

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

, forms. The bead is green while hot and blue when cold, so the cold colour is blue.

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