Which of the following is NOT true?

The correct answer is Option (3) → A superconductor is strongly attracted by a magnet.

Option (1) Bismuth, when kept in a magnetic field, moves from the stronger part of the field to the weaker part. — True. Bismuth is a diamagnetic material. Diamagnetic substances tend to move from the stronger to the weaker part of an external magnetic field.

Option (2) At STP, oxygen behaves as a paramagnetic substance. — True. Oxygen at STP is a paramagnetic material. It gets weakly magnetised along the field, and a magnet attracts it weakly.

Option (3) A superconductor is strongly attracted by a magnet. — Not true. A superconductor shows perfect diamagnetism. The field lines are completely expelled from it (\( \chi=-1 \)). So it repels a magnet, and the magnet also repels it. A magnet does not attract it.

NCERT (2026-27):
Diamagnetism – “The most exotic diamagnetic materials are superconductors. These are metals, cooled to very low temperatures which exhibits both perfect conductivity and perfect diamagnetism. Here the field lines are completely expelled! χ = –1 and μ_r = 0. A superconductor repels a magnet and (by Newton’s third law) is repelled by the magnet.”