amount of Al2S3 remains when 20.00 g of Al2S3 and 2.00 g of H2O are reacted?
...A few of the molar masses are as follows:

Al2S3 = 150.17 g/mol, H2O = 18.02 g/mol.

Al2S3(s) + 6 H2O(l) → 2 Al(OH)3(s) + 3 H2S(g)