It is hard. I did some searches before commenting and couldn't find anything about arsenic deficiency. I don't know much about arsenic biochemistry so could you kindly point us to a good source?

It's super easy with ChatGPT, for example. See my other reply in this thread, I've included the responses there.

Perhaps not. At the same time, when a person makes a claim, and several (or several hundred) people read it, it seems more efficient to ask the person who made the claim to supply the documentation, rather than making the several (hundred) people all do the looking. The looking does not have to be hard for this to be true.

Also, just in general debate terms, the one who makes a claim is the one who has the burden of substantiating it.