How much caffeine is there in decafinated coffee?

I assumed there was none but my husband claims there is some, although he is not sure how much.

Is it just a tiny bit?

5-10 milligrams in general, compared to around 200 in a normal cup

Caffiene, AFAIK, is usually removed by submitting the coffee beans to carbon dioxide at its triple point, in which caffiene is highly soluble. This means that caffeine leaves through a diffusion process and so some must always be left over.

I’m not aware of any other methods for decaffeination.