Which one of the following is a transition metal?

1. Architecture of the Modern Periodic Table (basic)

The Modern Periodic Table is the fundamental map of chemistry, organized not by weight, but by the atomic number (the number of protons in an atom's nucleus). This system ensures that elements with similar chemical properties fall into the same vertical columns. Think of it as a grand apartment complex for elements where their 'address' tells you exactly how they will behave. While most elements are solid at room temperature, there are unique exceptions like Mercury, which remains liquid Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.39.

The table is structured into a grid of 7 horizontal Rows (Periods) and 18 vertical Columns (Groups). Elements in the same Group share the same number of valence electrons (electrons in the outermost shell), which dictates their reactivity and how they form bonds Science, Class X (NCERT 2025 ed.), Carbon and its Compounds, p.60. For instance, Group 18 contains the stable Noble Gases, while Group 1 and 2 contain highly reactive metals like Magnesium (Mg) and Calcium (Ca).

The architecture is further divided into four distinct Blocks based on where the 'last' electron enters the atom's subshells:

Block	Groups	Nature of Elements
s-block	1 and 2	Highly reactive metals (Alkali and Alkaline Earth metals).
p-block	13 to 18	A mix of metals, metalloids, and non-metals.
d-block	3 to 12	Transition metals like Iron (Fe) and Zinc (Zn).
f-block	(Bottom rows)	Inner transition metals (Lanthanides and Actinides).

Understanding this layout is crucial for UPSC because it explains why certain elements are abundant in the Earth's crust. For example, Oxygen and Silicon are the most abundant elements by weight in the crust, followed by metals like Aluminium and Iron Physical Geography by PMF IAS, Earths Interior, p.53.

Sources: Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.39; Science, Class X (NCERT 2025 ed.), Carbon and its Compounds, p.60; Physical Geography by PMF IAS, Earths Interior, p.53

2. The s-block: Alkali and Alkaline Earth Metals (basic)

The s-block of the periodic table consists of elements in which the last electron enters the outermost s-orbital. This block is located on the extreme left of the table and includes two distinct families: Group 1 (Alkali Metals) and Group 2 (Alkaline Earth Metals). These elements are characterized by their high reactivity, as they only need to lose one or two electrons to achieve a stable, noble gas electron configuration. Because they lose electrons so easily, they are known as highly electropositive metals. While most metals are known for being hard and having high melting points, s-block elements like Sodium (Na) and Potassium (K) are surprisingly soft and can be cut with a knife. Although Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.39 notes that most metals exist as solids at room temperature and generally have high melting points, the s-block metals are exceptions due to their relatively weak metallic bonding. Their chemical reactivity is so high that they are never found free in nature; instead, they exist as compounds, such as Sodium Chloride (NaCl) or Magnesium Chloride (MgCl₂), which are major constituents of ocean salinity Physical Geography by PMF IAS, Ocean temperature and salinity, p.518. Beyond their chemistry, these elements are fundamental to life and the environment. In the field of agriculture, Calcium (Ca) and Magnesium (Mg) are classified as essential macronutrients that plants require in large quantities for healthy growth Environment, Shankar IAS Academy (10th ed.), Agriculture, p.363. Here is a quick comparison of the two groups within the s-block:

Feature	Group 1: Alkali Metals	Group 2: Alkaline Earth Metals
Examples	Lithium (Li), Sodium (Na), Potassium (K)	Beryllium (Be), Magnesium (Mg), Calcium (Ca)
Valency	+1 (loses 1 electron)	+2 (loses 2 electrons)
Reactivity	Extremely high (stored in oil)	High (less than Group 1)

Sources: Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.39; Physical Geography by PMF IAS, Ocean temperature and salinity, p.518; Environment, Shankar IAS Academy (10th ed.), Agriculture, p.363

3. The p-block: Non-metals and Post-Transition Metals (intermediate)

The p-block is perhaps the most diverse region of the periodic table, stretching from Group 13 to Group 18. It is unique because it is the only block that contains all three types of elements: metals, non-metals, and metalloids. While the s-block and d-block are entirely metallic, the p-block represents the transition from metallic character on the left to non-metallic character on the right. Within this block, we find post-transition metals (also known as 'poor metals') like Aluminium (Al), which sit between the transition metals and the metalloids. Unlike the transition metals (like Manganese or Iron) which have partially filled d-orbitals, post-transition metals have their d-orbitals completely filled, making them generally softer and having lower melting points than their d-block cousins. Aluminium is a standout member of the p-block. From a geographical perspective, it is the most abundant metal in the Earth's crust, making up about 8.1% of its weight Physical Geography by PMF IAS, Earths Interior, p.53. Chemically, it exhibits fascinating behavior. Most metals form basic oxides, but Aluminium forms an amphoteric oxide (Al₂O₃). This means it can react with both acids and bases to produce salt and water Science, class X (NCERT 2025 ed.), Metals and Non-metals, p.41. This versatility is a hallmark of elements located near the 'metalloid staircase' in the p-block. Moving further right in the p-block, we encounter essential non-metals like Oxygen and Silicon. These elements are the building blocks of the Earth's rocky exterior. In fact, Oxygen is the most abundant element in the Earth's crust by weight (46.6%), followed closely by Silicon (27.7%) Physical Geography by PMF IAS, Earths Interior, p.53. Understanding the p-block is crucial for UPSC aspirants because it bridges the gap between the heavy industrial metals of the d-block and the life-sustaining elements like Carbon, Nitrogen, and Oxygen.

Sources: Physical Geography by PMF IAS, Earths Interior, p.53; Science, class X (NCERT 2025 ed.), Metals and Non-metals, p.41

4. Industrial Applications: Ores and Minerals (intermediate)

In the study of chemistry and geography, understanding the distinction between elements based on their periodic table position and their industrial utility is crucial. While Manganese (Mn) and Aluminium (Al) are both vital industrial metals, they belong to different chemical families. Manganese is a transition metal (Atomic Number 25) located in the d-block. These elements are known for their incomplete d-subshells and variable oxidation states, making Manganese indispensable as a raw material for smelting iron ore and manufacturing ferro-alloys INDIA PEOPLE AND ECONOMY (NCERT 2025), Mineral and Energy Resources, p.55.

In contrast, Aluminium (Al) is a post-transition metal located in Group 13 of the p-block. Unlike Manganese, which is mined as various oxide ores often associated with the Dharwar geological system, Aluminium is commercially extracted from Bauxite. Bauxite is not a single mineral but a rock formed by the decomposition of various rocks rich in aluminium silicates Contemporary India II (NCERT 2022), Mineral and Energy Resources, p.110. Aluminium is prized for its unique combination of strength (comparable to iron) and extreme lightness, along with high conductivity.

Feature	Manganese (Mn)	Aluminium (Al)
Periodic Table Block	d-block (Transition Metal)	p-block (Post-transition Metal)
Primary Ore/Source	Manganese oxides (often in Dharwar system)	Bauxite (formed by rock decomposition)
Key Industrial Use	Iron smelting and Ferro-alloys	Aeronautics, electricals, and packaging
Leading Indian Producer	Odisha and Madhya Pradesh	Odisha (Kalahandi-Koraput belt)

Geographically, Odisha holds a dominant position for both minerals. For Manganese, the Bonai-Kendujhar belt is a major hub INDIA PEOPLE AND ECONOMY (NCERT 2025), Mineral and Energy Resources, p.55. For Bauxite, the Kalahandi-Koraput belt is the most significant deposit in India, contributing nearly half of the nation's total production Geography of India (Majid Husain), Resources, p.19. It is important to note that elements like Magnesium (Mg) and Calcium (Ca), which sound similar to Manganese, are actually alkaline earth metals found in the s-block (Group 2) and have very different chemical properties.

Sources: INDIA PEOPLE AND ECONOMY (NCERT 2025), Mineral and Energy Resources, p.55; Contemporary India II (NCERT 2022), Mineral and Energy Resources, p.110; Geography of India (Majid Husain), Resources, p.19

5. Alloys and Strategic Minerals (intermediate)

In the world of materials science, an alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal, combined to enhance specific properties. Unlike simple mixtures where you can see the ingredients, alloys are mixed so uniformly that they appear as a single, consistent substance Science Class VIII NCERT (Revised ed 2025), Nature of Matter, p.118. For instance, while pure copper is soft, mixing it with zinc creates brass, and mixing it with tin creates bronze—both far more durable than their parent metals.

Among the most critical alloying elements is Manganese (Mn), a transition metal found in the d-block of the periodic table. It is often called a 'strategic mineral' because of its indispensable role in the modern economy. Almost no steel can be made without it! Manganese serves two vital functions in steelmaking: it acts as a deoxidizing agent and it adds immense toughness. Remarkably, it takes approximately 10 kilograms of manganese to manufacture just one tonne of steel NCERT Class X Geography, Print Culture and the Modern World, p.108. Beyond steel, manganese is a workhorse in the production of dry-cell batteries, insecticides, and even paints.

Engineers 'tune' the properties of iron by adding different strategic minerals to create specific alloys for industrial needs. This customization allows us to build everything from delicate watch springs to massive warships. The table below illustrates how different elements transform the characteristics of iron:

Alloying Element	Primary Property Enhanced	Common Application
Chromium	Corrosion/Rust resistance	Stainless steel cutlery GC Leong, Manufacturing Industry, p.284
Manganese	Toughness and durability	Steam rollers and railway tracks
Nickel	Toughness and ductility	Armour plating for military use
Vanadium	High resilience	Heavy-duty springs
Tungsten	Raised melting point	High-speed cutting tools

Sources: Science Class VIII NCERT (Revised ed 2025), Nature of Matter: Elements, Compounds, and Mixtures, p.118; NCERT Class X Geography, Print Culture and the Modern World, p.108; Certificate Physical and Human Geography (GC Leong), Manufacturing Industry and The Iron and Steel Industry, p.284

6. Defining Transition Metals (d-block) (exam-level)

To understand the chemistry of the elements, we must look beyond just their names and dive into their electronic configurations. The d-block elements are those found in Groups 3 to 12 of the periodic table, where the d-orbitals are progressively filled. However, the term 'transition metal' has a more specific scientific definition: it refers to an element whose atom has a partially filled d-subshell, or which can form at least one stable ion with an incomplete d-subshell.

Take Manganese (Mn) as a classic example. With an atomic number of 25, its configuration ends in 3d⁵ 4s². Because that 3d subshell is only half-full, it fits the definition perfectly. This incomplete shell allows transition metals to exhibit unique properties like variable oxidation states and the formation of colored compounds. In contrast, metals like Magnesium (Mg) and Calcium (Ca) belong to the s-block (alkaline earth metals). These are highly reactive and never found free in nature Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.50. Similarly, Aluminium (Al) is a p-block metal. While these are all important metals in the activity series, they lack the d-orbital complexity of transition elements like Iron (Fe) or Copper (Cu) Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.55.

It is important to distinguish between "d-block elements" and "transition elements." While all transition elements are in the d-block, not all d-block elements are transition elements. For instance, Zinc (Zn) is in the d-block, but because it has a completely filled 3d¹⁰ subshell in both its neutral state and its common ionic state (Zn²⁺), some chemists strictly exclude it from the 'transition' category. These transition metals bridge the gap between the highly reactive s-block metals and the less metallic p-block elements, often serving as the backbone of metallurgy and industrial catalysis.

Sources: Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.50; Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.55

7. Solving the Original PYQ (exam-level)

Now that you have mastered the electronic configuration and the block-wise classification of the periodic table, this question serves as a direct application of those building blocks. To identify a transition metal, you must recall the specific definition: elements that belong to the d-block and possess an incomplete d-subshell in their neutral or common ionic states. This is where your understanding of the filling of orbitals (Aufbau principle) becomes crucial, as it allows you to distinguish between the highly reactive metals, the transition series, and the post-transition elements based on their position in the periodic table.

Applying this logic, we look at Manganese (Mn). With an atomic number of 25, its valence configuration is 3d⁵ 4s², clearly placing it in the first transition series of the d-block. It is the correct answer (B) because it perfectly fits the criteria of having partially filled d-orbitals, which also explains why it exhibits variable oxidation states—a hallmark of transition chemistry. When tackling such questions, I recommend you always visualize the bridge (the middle section) of the table where these d-block elements reside between the s and p blocks.

UPSC examiners often include distractors like Magnesium (Mg) and Calcium (Ca) because they sound phonetically similar to Manganese, but remember: these are alkaline earth metals located in Group 2 (s-block). Another common trap is Aluminium (Al); while it is a metal used in transition-like applications, it resides in Group 13 (p-block) and is technically a post-transition metal. Success in the Prelims often depends on your ability to resist these nomenclature traps by grounding your choice in the fundamental atomic structure rather than just familiar-sounding names. The Periodic Table of Elements (U.S. Department of Energy).