This is a bit of a trick question! A nickel is a coin, and the question is asking about the weight of a nickel, not the amount of a particular substance within it.

Here's the answer:

* A US nickel weighs 5 grams.

* There are 1000 milligrams (mg) in one gram (g).

Therefore, a nickel weighs 5000 milligrams (5 x 1000 = 5000).