Mr(O3) = 3Ar(O) = 3 * 16 = 48
Mr(FeO) = Ar(Fe) + Ar(O) = 56 + 16 = 72
Mr(CO) = Ar(C) + Ar(O) = 12 + 16 = 28
Mr(CuS) = Ar(Cu) + Ar(S) = 64 + 32 = 96
Mr(FeS2) = Ar(Fe) + 2Ar(S) = 56 + 2 * 32 = 120
Mr(NaOH) = Ar(Na) + Ar(O) + Ar(H) = 23 + 16 + 1 = 40
Mr(ZnCl2) = Ar(Zn) + 2Ar(Cl) = 65 + 2 * 35.5 = 136
Mr(NaBr) = Ar(Na) + Ar(Br) = 23 + 80 = 103
Mr(AlP) = Ar(Al) + Ar(P) = 27 + 31 = 58
Mr(BaCl2) = Ar(Ba) + 2Ar(Cl) = 137 + 2 * 35.5 = 208
Mr(NH3) = Ar(N) + 3Ar(H) = 14 + 3 = 17
Mr(NO2) = Ar(N) + 2Ar(O) = 14 + 2 * 16 = 46
Mr(NaNO3) = Ar(Na) + Ar(N) + 3Ar(O) = 23 + 14 + 3 * 16 = 85
Mr(Ca3N2) = 3Ar(Ca) + 2Ar(N) = 3 * 40 + 2 * 14 = 148