Mr (NaCl) = 23 + 35,5 = 58,5
Mr (Al2O3) = (27*2)+(16*3) = 102
Mr Mg(OH)2 = 24+(16+1)*2 = 58
Mr (H3PO4) = (1*3) + 31 + (16*4) = 98
Mr (CuS) = 64 + 32 = 86
Mr (NaCl) = 23 + 35,5 = 58,5
Mr (Al2O3) = (27*2)+(16*3) = 102
Mr Mg(OH)2 = 24+(16+1)*2 = 58
Mr (H3PO4) = (1*3) + 31 + (16*4) = 98
Mr (CuS) = 64 + 32 = 86