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Question:

The green colour produced in the borax bead test of a chromium (III) salt is due to:

CrB

Cr(BO2)3

Cr2O3

Cr2(B4O7)

Solution:

Correct option is C. Cr(BO2)3
In the borax bead test, metal oxide reacts with a glassy bead to form metaborates.
Na2B4O7.10H2O → Δ Na2B4O7 → Δ NaBO2 + B2O3
Cr2O3 + B2O3 → Δ Cr(BO2)3 (Green).
Hence, option C is correct.