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

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

JEE AdvancedJEE Advanced 2019

Solution:

In the borax bead test, metal oxide reacts with a glassy bead to form metaborates.
$Na _{2} B _{4} O _{7} \cdot 10 H _{2} O \xrightarrow{\Delta}Na _{2} B _{4} O _{7} \xrightarrow{\Delta}NaBO _{2}+ B _{2} O _{3}$
$Cr _{2} O _{3}+ B _{2} O _{3} \xrightarrow{\Delta} \underset{\text { Green }}{ Cr \left( BO _{2}\right)_{3}}$