a) Oxidation of ethylene : In presence of `Ag_2O`. See fig.1.

b) Expoxidation : Most important method of formation. It is the reaction in which an alkene is reacted with an organic peroxy acid or peracid such as per benzoic acid (`C_6H_5CO- O - OH`) or peracetic acid (`CH_3CO-O-OH`). See fig.2.

The epoxy bond angle is lower than that of normal tetrahedral bond angle `(l09^o28)`. There is strain in the ring due to the unstability. Due to this, epoxides are highly reactive towards nucleophilic substitution reaction (unlike ethers). They undergo ring opening reaction so as to release the strain. Epoxides undergo acid catalysed and base catalysed opening of the ring.

`text(Acid catalysed opening :)` The acid reacts with epoxides to prooduce a protonated epoxide. The protonated epoxide reacts with the weak nucleophile (water) to form protonated glycol , which then transfer a proton to a molecule of water to form the glycol and hydronium ion. See fig.1.

`text(Base Catalysed opening :)` Epoxides can also undergo base-catalysed ring opening provided the attacking nucleophile is also a strong base such as an alkoxide or hydroxide ion. See fig.2.