A metal at very low temperature has magnetic permeability μ = 0. It is a perfect
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → diamagnet
Inside a material \( B = \mu H \). A permeability \( \mu = 0 \) means B = 0 inside the metal for any applied field: the magnetic field is completely expelled. The relative permeability is \( \mu_r = 0 \) and the susceptibility is \( \chi = \mu_r - 1 = -1 \), the most negative value possible. This is perfect diamagnetism, shown by metals that become superconductors at very low temperatures (the Meissner effect).
NCERT (2026-27):
Points to Ponder – “… There exists a perfect diamagnet, namely, a superconductor. This is a metal at very low temperatures. In this case \( \chi = -1 \), \( \mu_r = 0 \), \( \mu = 0 \). The external magnetic field is totally expelled.”