W=Ar/Mr
Mr(Fe(OH)2) = 56*(16+1)*2=90
W(Fe)= 56/90*100%=62%
W(O)=16/90*100%=17%
W(H)=100-(62+17)=21%
Mr(CuSO4)=63,5+32+16*4=159,5
W(Cu)=63,5/159,5*100%=39%
W(S)=32/159,5*100%=20%
W(O)=100-(39+20)=41%
Mr(H3PO4)=1*3+31+16*4=98
W(H)=3/98*100%=3%
W(P)=31/98*100%=31%
W(O)=100-(31+3)=66%
Mr(MnO2)=55+16*2=87
W(Mn)=55/87*100%=63%
W(O)=32/87*100%=37%