Can you solve the MAGNET RIDDLE? ft YouTube CEO Susan Wojcicki

I would use the diamond file to scratch get some dust from one of the bars, and if they stick to the iron bar they came from, then it is iron. If I had a ring made from a non-ferrous metal, I can use the string to hang the ring then swing it across each of the bars, if the file mysteriously slows down when going past one bar, that bar is magnetic