When hydrogen and sulfur react, they form hydrogen sulfide, with the molecular formula H₂S.

Here's why:

* Hydrogen is in group 1 of the periodic table and has a valency of +1. This means it can form one bond.

* Sulfur is in group 16 of the periodic table and has a valency of -2. This means it can form two bonds.

To achieve a neutral compound, two hydrogen atoms (with a total positive charge of +2) are needed to bond with one sulfur atom (with a negative charge of -2). This results in the molecular formula H₂S.