Your question is Sock Box Puzzle. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
You have three boxes: one with infinite red socks, one with infinite black socks, and one with a mix. If all boxes are mislabeled, how can you determine the correct labels by picking only one sock?