a) M H3PO4=3*1 g/mol+31 g/mol+4*16 g/mol=98 g/mol
b) M Al2S3=2*27 g/mol+3*32 g/mol=150 g/mol
c) M CaCO3=40 g/mol+12 g/mol+3*16 g/mol=100 g/mol
