2Forming precipitates or complexes can strengthen reduction ability of the elemental substances; 2Ag+H2S->Ag2S(s)+H2(g) 2Ag 2H*+4I->2AgI,+H2 (g) 2Cu+2H*+4CS(NH2)2->2Cu[CS(NH2)2]2+H2(g) 硫脲 HCI 4M+O,+2H,O+8CN->4[M(CN)]+40H M=Cu,Ag,Au2Cu 2 H 4CS(NH ) 2Cu[CS(NH ) ] H (g) 2Ag 2 H 4 I 2AgI H (g) 2Ag H S Ag S(s) H (g) 2 2 2 2 2 2 2 - 2 2 2 2                HCl 硫脲 ②Forming precipitates or complexes can strengthen reduction ability of the elemental substances；    4MO2  2H2 O8CN 4[M(CN)2 ]  4OH M  C u, Ag, A u