Impure gold is leached with a dilute solution of sodium cyanide to form a soluble complex ‘X’ . ‘X’ when treated with zinc forms another complex ‘Y’ and precipitates gold. Oxidation state and coordination number of central metal in ‘Y’ is.

4Au+8NaCN+2H2O+O2→4Na[Au(CN)2](X)+4NaOH 2Na[Au(CN)2]+Zn→Na2[Zn(CN)4](Y)+2Auin [Au(CN)2]- .  .  .  oxidation state of ‘Au’ is + 1 and coordination number is twoin [Zn(CN)4]-2 .  .  . Oxidation state of 'Zn' is +2 and coordination number is four.