Metallurgy — Chemistry STD 12 — Question

• $4 Au ( s )+8 CN ^{-}( aq )+2 H _2 O _2( aq )+ O _2( g ) \rightarrow 4\left[ Au ( CN )_2\right]^{-}( aq )+4 OH ^{-}( aq )$
• $2\left[ Au ( CN )_2\right]^{-}( aq )+ Zn ( s ) \rightarrow 2 Au ( s )+\left[ Zn ( CN )_4\right]^{-2}( aq )$

In the first reaction $Au$ changes into $Au ^{+}$, i.e. its oxidation takes place. In the second reaction: $Au ^{+} \rightarrow Au ^{\circ}$
(i.e.) reduction takes place.