In an Ethernet link containing five routers with OSPF network interface type configured as broadcast, how many OSPF adjacencies are established on this Ethernet link?

With 5 routers on a broadcast segment, OSPF elects 1 DR and 1 BDR, leaving 3 DROthers; each DROther forms adjacencies with only the DR and BDR (not each other), yielding 1 DR-BDR + 3 DR-DROther + 3 BDR-DROther = 7 total adjacencies.

5 adjacencies is incorrect because it accounts for only one adjacency per router, ignoring that each DROther must maintain two adjacencies - one to the DR and one to the BDR.

10 is the full-mesh result using n*(n-1)/2 = 10 for 5 routers, which applies to non-broadcast or point-to-point OSPF network types where no DR/BDR is elected.

20 does not correspond to any valid OSPF adjacency calculation for 5 routers under any OSPF network type.

6 undercounts by one - the correct total of 1 DR-BDR adjacency plus 3 DR-DROther plus 3 BDR-DROther equals 7, not 6.