Verified answer

Mr(Cr2S3) = 52×2 + 32×3 = 168

Mr(BaCl2) = 137 + 35,5 × 2 = 208

Mr(Al3C4) = 27×3 + 12×4 = 129

Mr(Fe3O4) = 56×3 + 16×4 = 232

Mr(H2CO3) = 1×2 + 12 + 16×3 = 62