Mr(Al2O3) = 2Ar(Al) + 3Ar(O) = 2 * 27 + 3 * 16 = 102
Mr(BaCl2) = Ar(Ba) + 2Ar(Cl) = 137 + 2 * 35.5 = 208
Mr(HNO3) = Ar(H) + Ar(N) + 3Ar(O) = 1 + 14 + 3 * 16 = 63
Mr(Al2O3) = 2Ar(Al) + 3Ar(O) = 2 * 27 + 3 * 16 = 102
Mr(BaCl2) = Ar(Ba) + 2Ar(Cl) = 137 + 2 * 35.5 = 208
Mr(HNO3) = Ar(H) + Ar(N) + 3Ar(O) = 1 + 14 + 3 * 16 = 63