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Assertion : Coloured cations can be identified by borax bead test.
Reason : Transparent bead $(NaBO_2 + B_2O_3)$ forms coloured bead with coloured cation.
If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
If the Assertion is correct but Reason is incorrect.
If both the Assertion and Reason are incorrect.
Solution
Borax $(Na_2B_4O_7)$ when heated at about $740\,^oC$, forms a glassy bead which gives
different colour beads with different cations. Hence, it is used to identify cations in qualitative analysis. This test is called borax bead test.
$N{{a}_{2}}{{B}_{4}}{{O}_{7}}\,\xrightarrow{740\,{{\,}^{o}}C}\underbrace{\underset{\begin{smallmatrix}
\,\,\,\text{sodium } \\
\text{metaborate}
\end{smallmatrix}}{\mathop{2NaB{{O}_{2}}}}\,\,+\,\,\underset{\begin{smallmatrix}
\text{ boric} \\
anhydride
\end{smallmatrix}}{\mathop{{{B}_{2}}{{O}_{3}}}}\,}_{\text{glassy bead}}$
