What does ii mean?

2 grains. They don't really use grains any more. You still may see it for aspirin and a couple of other things so they want us to know it.

but why does it say 325mg? I tought it should be either grain or mg but not both. What does that prescription exactly mean?

Here is the full first part of the question:

"The nurse on the medical unit administers acetaminophen (Tylenol) with codeine #3 tab ii PO to a client. The physician ordered acetaminophen (Tylenol) 325 mg tab ii PO..."

"ii" does not mean "grains" -- it means two tablets, like a Roman numeral two (II), only with lower case "i"s instead of capitals. That gets used a lot in healthcare (in the US, I don't know about elsewhere). You usually see it handwritten as the two little verticals (or three, or iv for four or v for five) with a line over both of them together and two dots above -- but there's no way to do that when typing, so it would be typed as "ii" (or "iii", etc.)

(The abbreviation for "grains" would be "gr" with a Roman numeral -- in the case of Tylenol, it would be written "gr X" (ten grains, which approximates 650 mg).)

Exactly :)

Oh, I see what you mean. That's right. In that problem it would just mean two. It would be 2 grains only if it had a gr in front of it.