Amp rating with multiple 'mains'

Split bus panel, 100 amp service. Looks like that’s a conductor that has been disconnected.

Thanks everyone. I learned a lot.

One more question about this service. I included a photo of the meter showing the cable from the drop. This looks like it is wrapped and has no visible markings on it. It looks to be on the small side? Should anything about this cable be noted in an inspection report?

Thanks,
Jim