What was the most likely purpose of adding bovine serum albumin to the kinetics experiments in the passage bovine serum albumin a Reddit?

I often see bovine serum albumin (BSA) used in many questions or just albumin. I know that albumin is a protein in the blood (that I believe regulates the osmolarity of the blood?) But I was wondering what other significance there was to its use. When I see it is there anything I should be aware of or think of immediately?

(For example, you know if you see a question with protein structure and proline you know shits about to get fucked up...)

I was doing the SB for CP and there's a question asking why bovine serum albumin is used in the experiment (basically why was it added to the microwell plates and the choices are:

A) acts as a cocatalyst for the reaction B) prevents the esterase from adhering to the walls of the vessel C) helps buffer the solution from changes in pH D) is a non-specific target for protease contaminants

The explanation gives B as the answer and it says that it's "perfectly logical to assume [okay...] that albumin is added to maintain homogeneity and prevent the enzyme from adhering to the walls and other surfaces"

Were we supposed to know what BSA was? I can't extrapolate this from the passage. Thanks!

My second question is: There was also another question on the section bank that asked what is the Electron configuration of Cobalt 2+ and it lists it as [Ar]3s7.... what? how?? i thought the only exceptions were that for transition metals some things like chromium and copper when forming ions tend to favor the half-shell stability and such but why were the 2 electrons removed from 4s and not the 3s orbital? Because i know for s-block elements this is not the case (you just remove the ion from the most recent shell. Are there any other elements besides cobalt that do this?

EDIT: my apologies if these were already asked. Is there some sort of cumulative SB explanation thread with SB questions and answers by reddit people??

Anyone know (or at least have a good link) to an explanation of what BSA is? I see it in a lot of passages, and I know it is often explained in the passage, but I think it would be good to have some background information on it so I feel more comfortable with it.