Q. The drawing shows a bar magnet held in a clamp. A length of  cotton has  been used to  fasten a steel paper  clip  to  the  base  of  the  clamp stand. The paper clip is attracted to the magnet. Thin sheets of different metals are placed in the gap   between   the   magnet and paper clip.  Which one of them will prevent the magnet from attracting the paper clip?   Justify your answer with a scientific reason.