In my advanced classical physics course, it was stated that the electromagnetic field strength tensor $F_{\mu\nu} = \partial_{\nu}A_{\mu} - \partial_{\mu}A_{\nu}$ is invariant under "one-parameter" gauge transformations of the 4-vector potential: $A_{\mu} \to A_{\mu} + \partial_{\mu}\chi$. In a problem set, I was asked to show that there is no gauge transformation which imposes $A_{\mu} =0$.
My logic was the following: If there was such a transformation, this would require $\partial_{\mu}\chi = -A_{\mu}$, then we would have $F_{\mu\nu} = 0$, which is impossible in general (unless $F_{\mu \nu} = 0$ in EVERY gauge).
However, in the solution, it is stated that there is no such solution "because $\chi$ only carries one parameter". I understand that the condition would require 4 independent equations to be satisfied, but I don't understand immediately why is this not possible. I don't understand what is meant by a "one-parameter" transformation and I haven't found any useful information about this.
I would like to ask for clarification. In particular, I would like to understand what is meant by a "one-parameter" gauge transformation, and whether the given solution is consistent with/equivalent to my logic above.
As an extra, I would appreciate any short comments on whether (how) this "one-parameter" gauge transformation is related to one-parameter Lie groups?