Final answer:
The three OSPF states involved in forming an adjacency between two routers are Down, Init, and Two-way.
Step-by-step explanation:
The three OSPF states involved when two routers are forming an adjacency are: Down, Init, and Two-way.
In the Down state, the routers are not yet adjacent. In the Init state, the routers are exchanging initial information to establish adjacency.
Finally, in the Two-way state, the routers have successfully exchanged enough information to become adjacent.