Question

Which of the following is ferromagnetic.
(A) $Cu,Ag,Au$
(B) $Fe,Co,Ni$
(C) $Zn,Cd,Hg$
(D) $Ca,Sr,Ba$

Answer 1

First we know that the ferromagnetic substances are those substances which get strongly magnetised when placed in an external magnetic field. Hence, they are the substances which show permanent magnetism even in the absence of the magnetic field. Where the atoms of ferromagnetic substances have permanent dipole moment present in domains.

Complete Step By Step Answer:
Ferromagnetic substances can be permanently magnetised with the help of strong electrostatic fields. The metal ions of ferromagnetic substances are grouped together into small regions called domains in solid state. So that each domain acts as a small magnet.
Ferromagnetic substances exhibit a strong attraction to magnetic fields and are able to retain their magnetic properties after the external field has been removed. These substances have some unpaired electrons so their atoms have a net magnetic moment. Hence Iron ( $Fe$ ), nickel ( $Ni$ ), and cobalt ( $Co$ ) are examples of ferromagnetic materials.
Hence the correct option is (B) $Fe,Co,Ni$ .

Additional Information:
The magnetic substances are mainly classified into three types. They are diamagnetic substances, paramagnetic substances, and ferro magnetic substances.
Paramagnetic substances are substances which have unpaired electrons and they are weakly attracted by magnets. Examples: $C{u^{2 + }}$ , $F{e^{2 + }}$ are paramagnetic in nature. Whereas, diamagnetic substances are rarely magnetized when placed in a magnetic field. Magnetic dipoles in these substances tend to align in opposition to the applied field. Examples: Gold, mercury, and water.

Note:
Note that the ferromagnetic substances are strongly attracted by the magnetic field. Hence the ferromagnetic substances are strongly attracted towards a magnet. Also note that the strength of the magnets can be increased by increasing the temperature of the magnets or by exposing these magnets to external magnetic fields.