Reason : Transparent bead $(NaBO_2 + B_2O_3)$ forms coloured bead with coloured cation.
$N{{a}_{2}}{{B}_{4}}{{O}_{7}}\,\xrightarrow{740\,{{\,}^{o}}C}\underbrace{\underset{\begin{smallmatrix}
\,\,\,\text{sodium } \\
\text{metaborate}
\end{smallmatrix}}{\mathop{2NaB{{O}_{2}}}}\,\,+\,\,\underset{\begin{smallmatrix}
\text{ boric} \\
anhydride
\end{smallmatrix}}{\mathop{{{B}_{2}}{{O}_{3}}}}\,}_{\text{glassy bead}}$
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$2\left[ Au ( CN )_2\right]_{( aq )}^{-}+ Zn ( s ) \rightarrow 2 Au ( s )+\left[ Zn ( CN )_4\right]_{( aq )}^{2-}$
$A.$ Redox reaction
$B.$ Displacement reaction
$C.$ Decomposition reaction
$D.$ Combination reaction
Choose the correct answer from the options given below:
$\Delta {U_{BC}} = - 5\,kJ\,mo{l^{ - 1}},{q_{AB}} = 2\,kJ\,mo{l^{ - 1}}$
$\Delta {W_{AB}} = - 5\,kJ\,mo{l^{ - 1}},{W_{CA}} = 3\,kJ\,mo{l^{ - 1}}$
Heat absorbed by the system during process $CA$ is......$kJ\,mo{l^{ - 1}}$