what is allyl and how we can say the difference between allyl and alkyl

Allyl indicates a functional group with structural formula H2C=CH-CH2-R, where R is the rest of the molecule. It consists of methylene bridge (-CH2-) in between the vinyl group (-CH=CH2) and the rest of the molecule. Therefore, allyl group contains sp2 hybridized vinyl carbon atoms and sp3 hybridized allyl carbon atom. The allylic carbon atom is more reactive than normal alkanes, and it can easily form a stable carbocation because it is adjacent to vinyl carbon that can delocalize electrons to stabilize the positive charge.