`H_2S` is a gas while `H_2O` is liquid at room temperature·? Why ?

Explanation

Since atomic size of oxygen is less than sulphur and electronegativity of oxygen is more than sulphur, water show inter-molecular hydrogen bonding but hydrogen sulphide does not. As such large number of waters molecule are associated with each other to form a cluster molecules. Thus a large amount of energy is required for their separation. This energy is not available at room temperature. Thus `H_2O` is liquid and `H_2 S` is gas.

Due to the extensive hydrogen bonding in `H_2 O` boiling point of water is more than the boiling point of `H_2 S`.