Why H2O is a liquid (water) and H2S is a gas?
The reason is hydrogen bonding.

The relatively large electronegativity difference between oxygen and hydrogen (about 2.3) is the reason why the partially positively charged (try to think why they are partially positively charged) hydrogens are attracted to the lone pairs on the oxygen atoms of other water molecules.

The relatively smaller electronegativity difference between sulphur and hydrogen (about 0.5) is too small to polarise the covalent bond to a required extent. Secondly, the lone pairs on the sulphur atom are delocalised in the sp3 orbitals and the d orbitals - an option unavailable to oxygen. So, the “negative charge” of the lone pairs is also distributed and the interaction is lowered.

So, the hydrogen bonding in water causes the water molecules to be associated with each other due to intermolecular forces of attraction, whereas in the case of hydrogen sulphide, these forces of attraction area much weaker.

So, lesser energy is required to overcome the forces of interaction between the hydrogen sulphide molecules than those between water molecules. This energy is available at room temperature and hence, hydrogen sulphide is a gas, while water is still a liquid.