H2S is the analogous compound to H2O, structurally similar, but different chemical properties. Oxygen (O2) is a gas, sulfur at ambient conditions (S8) is a solid. If you look to either side of oxygen (nitrogen and fluorine) they possess respectively 3 and 1 electrons available for forming bonds.
the answer is Mol. concentration/time
Charcoal Filter is a type of filter containing charcoal to absorb the present impurities.