All the elements in a group (family) have a common valency. For example, all the elements of the carbon family (carbon, silicon, germanium, tin and lead) have common valency four. However, some of these elements can also have valency two. Which of the following can have valency two?

1. Organization of the Modern Periodic Table (basic)

The Modern Periodic Table is the fundamental map of chemistry, organizing 118 known elements not by their weight, but by their atomic number (the number of protons). This arrangement, based on the Modern Periodic Law, ensures that elements with similar chemical properties fall into the same vertical columns. The table is structured into 18 vertical Groups and 7 horizontal Periods. While a period indicates the number of electron shells an atom has, a group tells us about its valence electrons—the electrons in the outermost shell that dictate how an element reacts with others. For example, let us look at Group 14, also known as the Carbon Family. All elements in this group share a general electronic configuration of ns²np², meaning they have four electrons in their outermost shell. Generally, this leads to a valency of four. However, the organization of the table also reveals vertical trends. As we move down a group, the atoms get larger and the inner electrons provide a 'shielding' effect. In heavier elements like Germanium (Ge), Tin (Sn), and Lead (Pb), the two electrons in the 's' orbital become reluctant to participate in bonding—a phenomenon known as the Inert Pair Effect. This is why, while Carbon and Silicon almost always show a valency of 4, the heavier members can comfortably exhibit a valency of 2. Understanding this organization allows us to predict the reactivity of elements. For instance, the activity series shows that metals like Potassium (K) and Sodium (Na) are highly reactive, whereas others like Gold (Au) are least reactive Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.45. By knowing where an element sits in the table, we can immediately estimate its metallic character, its likely valency, and its chemical 'personality'.

Feature	Periods (Horizontal Rows)	Groups (Vertical Columns)
Total Number	7	18
What it represents	Number of occupied electron shells.	Number of valence (outer shell) electrons.
Chemical Properties	Change gradually across the period.	Are very similar within the same group.

Sources: Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.45

2. Electronic Configuration and Valence Shells (intermediate)

At the heart of chemistry lies a simple goal: stability. Elements react with one another because they are "seeking" a state of equilibrium, usually by mimicking the noble gases, which have a completely filled outermost shell Science, Class X, Metals and Non-metals, p.46. This outermost shell is known as the valence shell, and the electrons residing there are the ones that participate in chemical bonding. For instance, while Sodium (Na) has an electronic configuration of 2, 8, 1 and wants to lose one electron, Chlorine (Cl) is 2, 8, 7 and desperately seeks to gain one Science, Class X, Metals and Non-metals, p.47. This tendency to reach a stable octet (eight electrons) defines an element's chemical personality.

When we look at Group 14 of the periodic table (the Carbon family), we see a fascinating transition. These elements have a general electronic configuration of ns²np². This means they have four electrons in their valence shell. In the case of Carbon, it achieves stability by sharing these four electrons to form covalent bonds, reaching the configuration of Neon Science, Class X, Carbon and its Compounds, p.59. However, as we move down the group from Carbon (C) and Silicon (Si) toward heavier elements like Tin (Sn) and Lead (Pb), a phenomenon called the Inert Pair Effect begins to take hold.

The Inert Pair Effect occurs because, in heavier atoms, the two electrons in the s-orbital (the 'ns²' part) are held very tightly by the nucleus and become increasingly reluctant to participate in bonding. While Carbon and Silicon almost always show a valency of four (+4 state), the heavier members like Lead (Pb) often prefer to use only their two p-electrons for bonding, exhibiting a valency of two (+2 state). This is why the stability of the +2 oxidation state increases as you go down the group: Lead(II) compounds are much more common and stable than Lead(IV) compounds.

Element	Configuration	Dominant Valency
Carbon (C)	[He] 2s² 2p²	4 (Highly stable)
Silicon (Si)	[Ne] 3s² 3p²	4 (Highly stable)
Lead (Pb)	[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p²	2 (More stable than 4)

Sources: Science, Class X, Metals and Non-metals, p.46; Science, Class X, Metals and Non-metals, p.47; Science, Class X, Carbon and its Compounds, p.59

3. Group 14: The Carbon Family Overview (basic)

Welcome back! Today, we are exploring Group 14 of the Periodic Table, famously known as the Carbon Family. This group consists of Carbon (C), Silicon (Si), Germanium (Ge), Tin (Sn), and Lead (Pb). At the root of their behavior is their electronic configuration: ns²np². This means they have four electrons in their outermost shell. To achieve stability, they typically share these four electrons, a property known as tetravalency. As you might know, Carbon is the backbone of all living organisms because of this unique ability to form four strong covalent bonds Science, Class X (NCERT 2025 ed.), Carbon and its Compounds, p.77.

As we travel down the group from Carbon to Lead, we see a fascinating shift in personality. While Carbon is a classic non-metal, Silicon and Germanium act as metalloids (showing intermediate properties), and Tin and Lead are full-fledged metals Science, Class VIII, Nature of Matter, p.123. You will also notice a gradation in physical properties; as the atomic mass increases, their melting and boiling points change systematically Science, Class X (NCERT 2025 ed.), Carbon and its Compounds, p.67. One of Carbon's most extraordinary traits is catenation—the ability to form long, stable chains with itself. While Silicon can form chains of up to 7 or 8 atoms, they are quite reactive compared to the robust carbon-carbon bonds Science, Class X (NCERT 2025 ed.), Carbon and its Compounds, p.62.

A critical concept for your UPSC preparation is the Inert Pair Effect. While the group generally shows a +4 valency, the heavier elements (like Tin and Lead) become increasingly comfortable showing a +2 oxidation state. This happens because the two electrons in the 's' orbital (the ns² pair) become "inert" or reluctant to participate in bonding as the atom gets larger. Consequently, for Lead (Pb), the +2 state is actually more stable than the +4 state. This explains why we often see lead compounds like PbCl₂ rather than just PbCl₄.

Element	Type	Primary Oxidation State
Carbon (C)	Non-metal	+4
Silicon (Si)	Metalloid	+4
Germanium (Ge)	Metalloid	+4, +2
Tin (Sn)	Metal	+2, +4
Lead (Pb)	Metal	+2 (most stable)

Sources: Science, Class X (NCERT 2025 ed.), Carbon and its Compounds, p.77; Science, Class VIII, Nature of Matter: Elements, Compounds, and Mixtures, p.123; Science, Class X (NCERT 2025 ed.), Carbon and its Compounds, p.67; Science, Class X (NCERT 2025 ed.), Carbon and its Compounds, p.62

4. Effective Nuclear Charge and Screening Effect (intermediate)

To master the behavior of elements, we must first look at the internal 'tug-of-war' within an atom. The nucleus, containing positive protons, exerts an attractive force on negative electrons. However, in atoms with multiple shells, the outer electrons do not feel the full pull of the nucleus. This is due to the Screening Effect (or Shielding Effect). The inner-shell electrons act as a buffer, repelling the outer electrons and 'shielding' them from the nuclear charge. Just as a transparent medium can change the path or intensity of light passing through it Science, class X (NCERT 2025 ed.), Light – Reflection and Refraction, p.147, the intervening electrons dampen the 'signal' of the nuclear attraction before it reaches the valence shell.

The actual net positive charge experienced by an electron is known as the Effective Nuclear Charge (Zₑ𝒻𝒻). It is mathematically expressed as:

Zₑ𝒻𝒻 = Z - σ

Where Z is the atomic number (actual nuclear charge) and σ (sigma) is the shielding constant. Not all electrons shield equally; for instance, electrons in 's' orbitals are better at shielding than those in 'd' or 'f' orbitals. This difference in shielding ability is why some outer electrons are held more tightly than others, a concept that becomes vital when we study why heavier elements sometimes refuse to lose their outermost 's' electrons.

Factor	Screening Effect	Effective Nuclear Charge (Zₑ𝒻𝒻)
Core Definition	Repulsion by inner electrons that protects outer electrons.	The actual net attraction felt by an outer electron.
Trend Across a Period	Remains relatively constant (electrons added to same shell).	Increases (protons increase, but shielding doesn't keep up).
Effect on Atomic Size	Tends to push electrons away (increase size).	Pulls electrons closer (decrease size).

In a period (left to right), because the number of protons increases while the shielding remains nearly constant, the Zₑ𝒻𝒻 increases. This is the fundamental reason why atoms generally get smaller as you move from left to right across the periodic table. Conversely, as you go down a group, the increasing number of shells increases the screening effect, which counteracts the increase in nuclear charge, keeping the Zₑ𝒻𝒻 for valence electrons relatively stable, though the increased distance from the nucleus makes them easier to remove.

Sources: Science, class X (NCERT 2025 ed.), Light – Reflection and Refraction, p.147

5. Applications of Group 14: Semiconductors and Alloys (intermediate)

Group 14 elements, often called the Carbon Family, sit at a unique junction in the periodic table. They possess four valence electrons (general configuration ns²np²), which allows them to form four covalent bonds. However, their behavior changes dramatically as you move down the group. While Carbon is a non-metal famous for catenation—the ability to form long, stable chains—Silicon's ability to do so is limited to just seven or eight atoms before the compounds become highly reactive Science, Class X (NCERT 2025 ed.), Carbon and its Compounds, p.62. This difference is why Carbon is the backbone of life, while Silicon dominates the mineral world as the primary component of Quartz (SiO₂) and feldspar, which makes up half of the Earth's crust Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.175.

As we transition from non-metals to metals, we encounter Silicon (Si) and Germanium (Ge), which are classified as metalloids. These elements have intermediate electrical properties, making them the foundation of the semiconductor industry Science, Class VIII, Nature of Matter, p.123. Silicon is a poor conductor in its pure form at low temperatures but can be modified to conduct electricity under specific conditions, which is essential for manufacturing the microchips used in radios, radars, and computers.

Further down the group, we meet the heavier metals: Tin (Sn) and Lead (Pb). Here, a phenomenon called the Inert Pair Effect becomes significant. The two 's' electrons (ns²) become reluctant to participate in bonding because they are held more tightly by the nucleus. Consequently, while Carbon and Silicon almost always show a +4 oxidation state, Tin and Lead frequently exhibit a +2 oxidation state. This chemical flexibility is utilized in industrial applications. For instance, Solder is a crucial alloy made of Lead and Tin; it has a remarkably low melting point, allowing it to be used for welding electrical wires without damaging the components Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.54.

Lead, in particular, is valued for its high density, malleability, and poor heat conductivity. This makes it ideal for lead sheeting, cable covers, and paints, though its primary modern use is in lead-acid batteries for automobiles and aircraft Environment and Ecology by Majid Hussain, Distribution of World Natural Resources, p.33. Understanding Group 14 is essentially about tracking the shift from the organic chemistry of carbon to the high-tech electronics of silicon and the heavy industrial metallurgy of lead.

Sources: Science, Class X (NCERT 2025 ed.), Carbon and its Compounds, p.62; Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.175; Science, Class VIII (NCERT Revised ed 2025), Nature of Matter, p.123; Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.54; Environment and Ecology by Majid Hussain, Distribution of World Natural Resources, p.33

6. The Inert Pair Effect and Oxidation States (exam-level)

To understand why certain elements behave differently as we move down the periodic table, we must look at their electronic configuration. Elements in the Carbon family (Group 14) have four electrons in their outermost shell, specifically ns²np². Under normal circumstances, you would expect these elements to use all four electrons to form bonds, resulting in a +4 oxidation state. While this is the rule for Carbon and Silicon, things change significantly as the atoms get heavier. As we descend from Germanium (Ge) to Tin (Sn) and finally to Lead (Pb), a phenomenon known as the Inert Pair Effect takes hold. This occurs because the two electrons in the s-orbital (ns²) are drawn more tightly toward the nucleus. This happens because the intervening d and f orbitals (which appear in heavier elements) are quite 'diffuse' and do not shield the s-electrons effectively from the nucleus's positive charge. Consequently, these s-electrons become 'inert' or reluctant to participate in bonding, leaving only the two p-electrons available. This explains why heavier elements like Lead often exhibit a valency of two instead of four Science, class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.14. The stability of these oxidation states follows a very clear trend: the +4 state becomes less stable as you go down the group, while the +2 state becomes more stable. For example, while Carbon almost always prefers +4, Lead (Pb) is much more stable in the +2 state. This is why we frequently encounter Lead(II) oxide (PbO) in chemical reactions Science, class X (NCERT 2025 ed.), Metals and Non-metals, p.41. Understanding this shift is crucial for predicting how these metals will react with oxygen or acids to form various compounds.

Element Group Position	Dominant Oxidation State	Reasoning
Top (C, Si)	+4	All 4 valence electrons (ns²np²) participate in bonding.
Middle (Ge, Sn)	+4 and +2	Transition phase; both states are observable.
Bottom (Pb)	+2	Inert Pair Effect; s-electrons stay close to the nucleus.

Sources: Science, class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.14; Science, class X (NCERT 2025 ed.), Metals and Non-metals, p.41

7. Solving the Original PYQ (exam-level)

To solve this question, you must synthesize your knowledge of atomic structure with the periodic trends of Group 14 elements. While you have learned that the general electronic configuration of the carbon family is ns²np² (suggesting a standard valency of four), this question tests your understanding of the Inert Pair Effect. This phenomenon occurs as you move down a group: the two electrons in the s-orbital become increasingly reluctant to participate in bonding because they are more effectively pulled by the nucleus. This leaves only the two p-electrons available, resulting in a stable valency of two for the heavier members of the family.

Walking through the logic, we start with Carbon and Silicon, which almost exclusively exhibit a valency of four because their s and p electrons are relatively close in energy. However, as we descend to Germanium (Ge), Tin (Sn), and Lead (Pb), the stability of the +2 oxidation state increases significantly. Germanium begins to show this divalent character in specific compounds, while for Tin and Lead, the +2 state is common and, in the case of Lead, even more stable than the +4 state. Therefore, the correct answer is (C) Germanium, tin and lead, as these three elements represent the transition where the inert pair effect becomes chemically significant Coordination Chemistry Reviews.

UPSC often uses "only" as a distractor trap to test the depth of your conceptual clarity, as seen in options (B) and (D). Many students correctly identify Tin and Lead but overlook Germanium because its +2 state is less common in introductory texts. Furthermore, option (A) is incorrect because Silicon is too high in the group for the inert pair effect to manifest; its valence electrons are not shielded enough to prevent the s-orbital from participating in bonding. By recognizing that the trend of lower valency stability increases progressively down the group, you can avoid these narrow traps and confidently select the more inclusive, scientifically accurate option.