In OSPF Multi Area, all area must be connected to the backbone area (area 0), in order to communicate each other. Inter area routing will through the backbone area (area 0). If there’s area that isn’t connected to the backbone area we can setup a virtual link.
Based on topology above, area 2 doesn’t have connection/route to other area, since it’s not connected to the backbone area (area 0).
In this case, we can setup a Virtual Link from R4 to R2 and vice versa, from R2 to R4.