Ethylene oxide when treated with Grignard reagent yields :

Ethylene oxide (oxirane) undergoes nucleophilic ring opening upon attack by a Grignard reagent ($\text{RMgX}$). The nucleophilic 'R' group attacks the less hindered carbon, forming an alkoxide intermediate ($\text{R}-{\text{CH}}_2-{\text{CH}}_2-{\text{O}}^{-}{\text{MgX}}^{+}$), which on subsequent acid hydrolysis gives a primary alcohol ($\text{R}-{\text{CH}}_2-{\text{CH}}_2-\text{OH}$) containing two carbon atoms more than the original Grignard reagent.