Question

Which of the following substances is weakly attracted in the magnetic field?
1. CrO₂
2. H₂O
3. C₆H₆
4. O₂

Answer 1

Correct Answer - Option 4 : O₂

Concept:

Magnetic properties:

• Every substance has some magnetic properties associated with it.
• The origin of these properties lies in the electrons.
• Each electron in an atom behaves like a tiny magnet. Its magnetic moment originates from two types of motions  (i) its orbital motion around the nucleus and (ii) it's spin around its own axis.
• Electron being a charged particle and undergoing these motions can be considered as a small loop of current that possesses a magnetic moment.
• Thus, each electron has a permanent spin and an orbital magnetic moment associated with it.
• The magnitude of this magnetic moment is very small and is measured in the unit called Bohr magneton,\({{{\mu }}_{_{\text{B}}}}\). It is equal to 9.27 × 10^–24 A m².
• On the basis of their magnetic properties, substances can be classified into five categories:

(i) paramagnetic (ii) diamagnetic (iii) ferromagnetic (iv) antiferromagnetic and (v) ferrimagnetic

Explanation:

Given below are the characteristic properties and examples of paramagnetic, diamagnetic, ferromagnetic substances.

Paramagnetic	Diamagnetism	Ferromagnetism
They are weakly attracted by a magnetic field.	They are weakly repelled by a magnetic field.	They are attracted very strongly by a magnetic field.
They are magnetized in a magnetic field in the same direction.	They are weakly magnetized in a magnetic field in opposite direction.	When the substance is placed in a magnetic field all the domains get oriented in the direction of the magnetic field.
They lose their magnetism in the absence of a magnetic field.	The pairing of electrons cancels their magnetic moments and they lose their magnetic character.	These substances can be permanently magnetized. This magnetism persists even when the magnetic field is removed.
Paramagnetism is due to the presence of one or more unpaired electrons that are attracted by the magnetic field.	Diamagnetism is shown by those substances in which all the electrons are paired and there are no unpaired electrons.	In a solid-state, the metal ions of ferromagnetic substances are grouped together into small regions called domains. Thus, each domain acts as a tiny magnet.
Eg: O2, Cu2+, Fe3+, Cr3+ etc,.	Eg: H2O, NaCl, C6H6	Eg: Iron, cobalt, nickel, gadolinium, and CrO2.

• CrO₂ ⇒ Ferromagnetic ⇒ strongly attracted by the magnetic field
• H2O ⇒ Diamagnetic ⇒ Weakly repelled by the magnetic field
• C6H6 ⇒ Diamagnetic ⇒ Weakly repelled by the magnetic field
• O2 ⇒ Paramagnetic ⇒ They are weakly attracted by a magnetic field.

Hence, O2 is the substance weakly attracted by the magnetic field among the given substances.

Antiferromagnetism:

• Substances like showing antiferromagnetism have domain structure similar to ferromagnetic substance, but their domains are oppositely oriented and cancel out each other's magnetic moment.
• Eg. MnO etc.

Ferrimagnetism:

• Ferrimagnetism is observed when the magnetic moments of the domains in the substance are aligned in parallel and anti-parallel directions in unequal numbers.
• They are weakly attracted by a magnetic field as compared to ferromagnetic substances.
• These substances also lose ferrimagnetism on heating and become paramagnetic
• Eg: Fe₃O₄(magnetite) and ferrites like MgFe₂O₄ and ZnFe₂O₄ are examples of such substances.