Mention 4 elements which exhibit allotropy?
Carbon, Oxygen, Phosphorus, Silicon
Carbon- has plenty of allotropes, including Diamond, Graphite, Graphene, fullerene... All of which have unique properties with a range of uses.
Oxygen has the standard
Phosphorus has a few allotropes as well, one of the most famous (or infamous) being White Phosphorus
Silicon is normally in a crystalline structure, but there is such a thing Amorphous silicon which is used in a variety of electronic devices due to its ability to act as a semiconductor.