\(a,CTHH\left(A\right):MO\\ PTK_{MO}=NTK_M+16=3NTK_{Al}=81\left(đvC\right)\\ \Rightarrow NTK_M=65\left(đvC\right)\\ \Rightarrow M\text{ là kẽm }\left(Zn\right)\\ b,CTHH\text{ hợp chất: }MCl_2\\ PTK_{MCl_2}=NTK_M+2\cdot35,5=3,4\cdot PTK_{CuO}\\ \Rightarrow NTK_M+71=3,4\cdot80=272\\ \Rightarrow NTK_M=210\left(đvC\right)\\ \Rightarrow M\text{ là thủy ngân }\left(Hg\right)\)