Which one of the following is paramagnetic in nature ?

1. Atomic Structure and Electron Arrangement (basic)

At the heart of chemistry lies the atomic structure. Every atom consists of a central nucleus containing protons and neutrons, surrounded by electrons that reside in specific energy levels called shells (K, L, M, N). For a UPSC aspirant, the most critical part of this structure is the valence shell—the outermost orbit. The number of electrons in this shell determines how an element will behave, react, and bond with others Science, Carbon and its Compounds, p.60.

Why do atoms react at all? They are driven by a quest for stability. An atom is most stable when its outermost shell is completely full, a state known as the noble gas configuration. For most elements, this means having eight electrons in the outer shell, often called the octet rule Science, Carbon and its Compounds, p.59. Elements achieve this stability in two primary ways:

• Ionic Bonding: Atoms like Sodium (Na) or Chlorine (Cl) completely transfer electrons. If an atom loses an electron, it becomes a positively charged cation; if it gains one, it becomes a negatively charged anion Science, Metals and Non-metals, p.46.
• Covalent Bonding: Some atoms, like Carbon, find it difficult to fully lose or gain four electrons. Instead, they share electrons with other atoms to complete their octets, forming molecules like CO₂ or N₂ Science, Carbon and its Compounds, p.59-60.

To visualize these arrangements, we use electron dot structures. In these diagrams, we represent only the valence electrons as dots around the element's symbol. For instance, in a molecule of Nitrogen (N₂), each nitrogen atom has five valence electrons and shares three pairs to reach the magic number of eight, creating a triple bond Science, Carbon and its Compounds, p.60.

Feature	Cation	Anion
Charge	Positive (+)	Negative (–)
Electron Action	Loses valence electrons	Gains valence electrons
Example	Na → Na⁺ + e⁻	Cl + e⁻ → Cl⁻

Sources: Science, Carbon and its Compounds, p.59; Science, Carbon and its Compounds, p.60; Science, Metals and Non-metals, p.46

2. Classification of Magnetic Materials (intermediate)

At the heart of every material are electrons, which act like tiny spinning magnets due to their spin and orbital motion. Whether a substance is attracted to or repelled by a magnetic field depends entirely on how these electrons are arranged. When we look at the periodic table, we classify materials into three primary categories based on this atomic-level behavior: Diamagnetic, Paramagnetic, and Ferromagnetic.

Diamagnetism is a property of materials where all electrons are paired. Because electrons in a pair spin in opposite directions, their magnetic effects cancel each other out. Consequently, diamagnetic substances like Dihydrogen (H₂), Nitrogen (N₂), and even water are very weakly repelled by magnetic fields. In contrast, Paramagnetism arises when an atom or molecule possesses one or more unpaired electrons. These unpaired electrons create a net magnetic moment that is weakly attracted to an external magnetic field. A classic example is Molecular Oxygen (O₂), which contains two unpaired electrons, making it paramagnetic.

The most intense form of magnetism is Ferromagnetism. In these materials, the magnetic moments of many atoms align in the same direction within regions called 'domains.' Even a weak external field can cause these domains to align perfectly, leading to a very strong attraction. Metallic Iron (Fe) is the quintessential example of a ferromagnetic material at room temperature. This property is why iron filings are so easily separated from other non-magnetic substances using a simple magnet Science, Class VIII (NCERT), Nature of Matter: Elements, Compounds, and Mixtures, p.128. Furthermore, because iron can concentrate magnetic lines of force so effectively, it is frequently used as a core to strengthen the field of an electromagnet Science, Class VIII (NCERT), Electricity: Magnetic and Heating Effects, p.50.

Property	Diamagnetic	Paramagnetic	Ferromagnetic
Electron Status	All electrons are paired	At least one unpaired electron	Unpaired electrons aligned in domains
Effect of Magnet	Weakly repelled	Weakly attracted	Strongly attracted
Examples	H₂, N₂, Gold, Water	O₂, Aluminum, Platinum	Iron (Fe), Cobalt (Co), Nickel (Ni)

Sources: Science, Class VIII (NCERT), Nature of Matter: Elements, Compounds, and Mixtures, p.128; Science, Class VIII (NCERT), Electricity: Magnetic and Heating Effects, p.50

3. Ferromagnetism: Iron and Transition Metals (basic)

When we talk about magnetism in the context of the periodic table, Iron (Fe) is the gold standard. While many elements show weak magnetic properties, iron belongs to a special elite club of materials that exhibit Ferromagnetism. This is the strongest form of magnetism, where a material is not just weakly influenced by a magnetic field, but can actually be permanently magnetized or strongly attracted to a magnet, as seen with iron filings forming distinct patterns Science, Class X (2025 ed.), Magnetic Effects of Electric Current, p.196.

What makes iron and certain other transition metals (like Cobalt and Nickel) so special? It comes down to their atomic structure. In these elements, there are unpaired electrons in their outer shells. However, ferromagnetism is a "team sport." In a block of iron, the magnetic fields of individual atoms align themselves in the same direction within small regions called magnetic domains. When an external magnetic field is applied, these domains line up perfectly, creating a powerful collective force. This is why iron is used as a core to make electromagnets significantly stronger Science, Class VIII (2025 ed.), Electricity: Magnetic and Heating Effects, p.50.

Feature	Paramagnetism	Ferromagnetism
Strength	Very weak attraction	Very strong attraction
Persistence	Lost when the magnet is removed	Can become a permanent magnet
Mechanism	Individual unpaired electrons	Aligned "Domains" of many atoms

Interestingly, this magnetic property is tied to the elemental state of the metal. If iron reacts chemically to form a compound, such as iron sulfide (FeS), the arrangement of its electrons changes completely. In FeS, the iron and sulfur atoms are chemically bonded, and the resulting black mass is no longer attracted to a magnet Science, Class VIII (2025 ed.), Nature of Matter: Elements, Compounds, and Mixtures, p.128. This proves that magnetism in transition metals is highly dependent on how their electrons are shared or structured in a solid lattice.

Sources: Science, Class X (2025 ed.), Magnetic Effects of Electric Current, p.196; Science, Class VIII (2025 ed.), Electricity: Magnetic and Heating Effects, p.50; Science, Class VIII (2025 ed.), Nature of Matter: Elements, Compounds, and Mixtures, p.128

4. Inert Gases and Triple Bonds: Nitrogen and Hydrogen (intermediate)

In the quest for chemical stability, atoms strive to achieve a noble gas configuration—a state where their outermost electron shell is completely filled. While carbon is the famous "versatile element" that achieves this through various bonds Science, Carbon and its Compounds, p.77, simpler molecules like Hydrogen (H₂) and Nitrogen (N₂) illustrate the power of the covalent bond. A covalent bond is formed by the sharing of electron pairs between two atoms Science, Carbon and its Compounds, p.60. However, the number of shared pairs drastically changes how the element behaves in our atmosphere.

Hydrogen atoms share just one pair of electrons, forming a single bond. Nitrogen, on the other hand, has five valence electrons and needs three more to be stable. To achieve this, two nitrogen atoms share three pairs of electrons, creating a powerful triple bond. This triple bond is exceptionally strong and difficult to break, which is why Nitrogen is described as a relatively inert gas Physical Geography by PMF IAS, Earths Atmosphere, p.272. It doesn't like to react with other substances under normal conditions, unlike oxygen, which is highly reactive and promotes combustion.

Feature	Dihydrogen (H₂)	Dinitrogen (N₂)
Bond Type	Single Covalent Bond	Triple Covalent Bond
Reactivity	Flammable/Reactive	Relatively Inert (Inactive)
Key Role	Fuel/Reduction	Diluting Oxygen/Preventing Rancidity

This "inertness" makes Nitrogen invaluable in daily life. Because it does not easily react with oils or fats, it is used to flush chip packets to prevent rancidity (oxidation) Physical Geography by PMF IAS, Earths Atmosphere, p.272. Similarly, it is used in electric bulbs to protect the tungsten filament from burning up in the presence of oxygen. While it stays "quiet" in the air, certain soil bacteria and algae have the unique ability to break this triple bond through nitrogen fixation, converting it into forms plants can actually use for growth Environment and Ecology, Major Crops and Cropping Patterns in India, p.116.

Sources: Science, NCERT 2025 ed., Chapter 4: Carbon and its Compounds, p.60, 77; Physical Geography by PMF IAS, Earths Atmosphere, p.272; Environment and Ecology, Majid Hussain, Major Crops and Cropping Patterns in India, p.116

5. Modern Applications: Superconductors and Maglev (exam-level)

At the heart of modern high-tech engineering lies the phenomenon of superconductivity. In a standard conductor, such as the copper wire used in simple circuits, electricity flows but encounters electrical resistance, which generates heat as a byproduct. However, certain materials, when cooled below a specific Critical Temperature (Tc), undergo a phase transition where their resistance drops to exactly zero. This means an electric current could circulate in a superconducting loop forever without any power source. This leap in efficiency is a hallmark of what we define as high-tech industry, characterized by intensive research and development Fundamentals of Human Geography, Class XII NCERT, Secondary Activities, p.42.

The most visually stunning application of this concept is Magnetic Levitation (Maglev). This relies on the Meissner Effect: the ability of a superconductor to expel all internal magnetic fields. While we know that electricity and magnetism are deeply linked—where a current creates a magnetic field Science, Class X NCERT, Magnetic Effects of Electric Current, p.195—superconductors take this relationship further. When a magnet is placed over a superconductor, the superconductor creates mirror-image magnetic poles that perfectly repel the magnet, allowing it to float. In Maglev trains, this eliminates mechanical friction entirely, allowing for incredible speeds and smooth transit.

From the perspective of the periodic table, many pure elements like Mercury (Hg), Lead (Pb), and Niobium (Nb) exhibit these properties at extremely low temperatures. Modern research, much of which is conducted at centers of excellence like the Indian Institutes of Technology (IITs) History, Class XII Tamilnadu State Board, Envisioning a New Socio-Economic Order, p.126, focuses on finding "High-Temperature Superconductors." These are materials that can reach a superconducting state using liquid nitrogen rather than expensive liquid helium, making technologies like powerful MRI machines and lossless power grids commercially viable.

Sources: Fundamentals of Human Geography, Class XII NCERT, Secondary Activities, p.42; Science, Class X NCERT, Magnetic Effects of Electric Current, p.195; History, Class XII Tamilnadu State Board, Envisioning a New Socio-Economic Order, p.126

6. The Oxygen Anomaly: Unpaired Electrons (exam-level)

When we look at the Lewis Dot Structures of common gases, we see that atoms share electrons to achieve a stable octet. For instance, an oxygen atom (Atomic Number 8) has six electrons in its L shell and needs two more to be stable Science, Class X (NCERT 2025 ed.), Chapter 4, p.60. This results in a double bond (O=O) where four electrons are shared. On the surface, it looks like every electron has a partner. However, oxygen hides a fascinating "anomaly": it is paramagnetic. This means that despite appearing fully paired in simple diagrams, molecular oxygen (O₂) actually possesses two unpaired electrons in its higher energy levels, causing it to be weakly attracted to magnetic fields.

To understand the significance of this, we must compare it to its neighbors in the periodic table. Most common diatomic molecules are diamagnetic, meaning all their electrons are paired up and they are slightly repelled by magnetic fields. Nitrogen (N₂), for example, involves a triple bond where each nitrogen atom contributes three electrons to the shared pool Science, Class X (NCERT 2025 ed.), Chapter 4, p.60. Because all these electrons are tightly paired, N₂ shows no magnetic attraction. Similarly, dihydrogen (H₂) and water (H₂O) have all their valence electrons paired in bonds or lone pairs, making them diamagnetic as well.

It is also crucial to distinguish this weak attraction from the strong magnetism we see in metals like Iron (Fe). While oxygen is paramagnetic (weakly attracted), metallic iron is ferromagnetic, meaning it can form permanent magnets and shows a much more powerful response to magnetic fields. This distinction is a classic favorite in competitive exams because it challenges the assumption that only solids can be magnetic.

Property	Paramagnetism (e.g., O₂)	Diamagnetism (e.g., N₂, H₂)
Electron Status	One or more unpaired electrons.	All electrons are paired.
Magnetic Behavior	Weakly attracted by a magnetic field.	Weakly repelled by a magnetic field.

Sources: Science, Class X (NCERT 2025 ed.), Chapter 4: Carbon and its Compounds, p.60

7. Solving the Original PYQ (exam-level)

Now that you have mastered the fundamentals of electron configuration and magnetic behaviors, this question tests your ability to apply those molecular orbital concepts to real-world elements. The core principle to remember is that paramagnetism requires the presence of unpaired electrons within the atom or molecule. While most simple diatomic molecules pair their electrons to achieve stability, Science, Class XI (NCERT) explains that Oxygen (O2) is a unique exception; its molecular structure contains two unpaired electrons in its antibonding orbitals, making it weakly attracted to magnetic fields. This specific electronic arrangement is what defines it as paramagnetic.

To arrive at the correct answer, you must navigate a classic UPSC trap: the distinction between ferromagnetism and paramagnetism. Iron (A) is often the first choice for students because of its strong magnetic properties, but it is actually ferromagnetic, meaning it can form permanent magnets—a much stronger state than the weak, temporary attraction of paramagnetism. Meanwhile, Hydrogen (B) and Nitrogen (D) are diamagnetic because their electrons are completely paired in single and triple covalent bonds, respectively, as detailed in Science, Class X (NCERT). Therefore, by understanding the specific sub-atomic 'rules' of electron pairing, we see that Oxygen is the only choice that fits the precise definition of a paramagnetic substance.