In article ,
says...

The reason that gold is used is that it is more resistant than any
other of the noble metals to 'dissolving' into anything, forming an
oxide or otherwise degrading. If it is attacked by something, that
something will be quite toxic or dangerous in its own right. Those
compounds would include chlorine, mercury, cyanide and reactants of
same.

I think I have mentioned "purple plague" here before.
https://en.wikipedia.org/wiki/Gold-a..._intermetallic. I learnt
about it decades ago when working on experimental conducting films.

I thought that gold was tricky to solder precisely because it did tend
to dissolve unless the solder was already loaded with gold.

Mike.