Which one among the following is not a property of salt?

1. Chemical Bonding: Ionic vs Covalent Bonds (basic)

Atoms are rarely found alone in nature; they seek stability by interacting with other atoms. This stability is usually achieved when an atom attains a noble gas configuration (a full outer shell of electrons). The 'glue' that holds these atoms together is known as a chemical bond, which is driven by interparticle attractions. Science, Class VIII, Particulate Nature of Matter, p.101. Understanding the nature of these bonds helps us predict how a substance will behave—whether it will melt easily, dissolve in water, or conduct electricity. There are two primary ways atoms achieve this stability:

• Ionic Bonding: This occurs through the complete transfer of one or more electrons from one atom to another. One atom becomes a positively charged ion (cation) and the other a negatively charged ion (anion). Because 'unlike charges attract,' a powerful electrostatic force binds them together. Science, Class VIII, Exploring Forces, p.71. These compounds, like Sodium Chloride (NaCl), typically form an ordered crystalline lattice.
• Covalent Bonding: In many cases, atoms find it too 'energetically expensive' to fully give up or gain electrons. Instead, they share their valence electrons. Science, Class X, Carbon and its Compounds, p.59. In a molecule like H₂O, the shared electrons 'belong' to the outer shells of both atoms simultaneously, tying them together in a covalent bond.

Feature	Ionic Bonds	Covalent Bonds
Mechanism	Transfer of electrons.	Sharing of electrons.
Forces	Strong electrostatic attraction.	Sharing of electron pairs.
Melting Point	High (requires massive energy to break the lattice).	Generally Lower.
Conductivity	Conducts when molten or dissolved (ions are free to move).	Generally poor conductors (no free ions).

Ionic compounds are also famously brittle. While the electrostatic forces are strong, a sharp blow can shift the ions in the lattice. If like-charges (positive next to positive) align even for a moment, they repel each other instantly, causing the crystal to shatter. Science, Class X, Metals and Non-metals, p.49.

Sources: Science, Class VIII, Exploring Forces, p.71; Science, Class VIII, Particulate Nature of Matter, p.101; Science, Class X, Carbon and its Compounds, p.59; Science, Class X, Metals and Non-metals, p.49

2. Formation and Nature of Ionic Compounds (basic)

To understand the nature of matter, we must look at how atoms interact to find stability. Ionic compounds (also known as electrovalent compounds) are formed through a "give-and-take" relationship between atoms. Specifically, they are created when a metal transfers one or more electrons to a non-metal. Science, class X (NCERT 2025 ed.), Metals and Non-metals, p.48. This transfer results in the formation of ions—atoms that carry an electric charge.

When an atom loses an electron, it becomes a positively charged cation (because it now has more protons than electrons). Conversely, an atom that gains an electron becomes a negatively charged anion. Physical Geography by PMF IAS, Thunderstorm, p.348. For example, in the formation of Sodium Chloride (NaCl), the sodium atom loses an electron to become Na⁺, while the chlorine atom gains that electron to become Cl⁻. Because these two ions have opposite charges, they are pulled together by powerful electrostatic forces of attraction. Science, class X (NCERT 2025 ed.), Metals and Non-metals, p.47.

One of the most important things to realize is that ionic compounds do not exist as simple, isolated molecules. Instead, they form aggregates—vast, repeating 3D structures called crystalline lattices. This unique structure dictates their physical behavior:

Feature	Nature of Ionic Compounds
Melting & Boiling Points	Very high. A massive amount of thermal energy is needed to overcome the strong electrostatic bonds in the lattice. Science, class X (NCERT 2025 ed.), Carbon and its Compounds, p.59.
Physical State	They are solids and generally brittle. When pressure is applied, like-charged ions may align and repel each other, causing the crystal to shatter.
Electrical Conductivity	They do not conduct electricity in solid form because ions are fixed. However, they are excellent conductors in a molten state or when dissolved in water, as the ions become free to move. Science, class X (NCERT 2025 ed.), Carbon and its Compounds, p.59.

Sources: Science, class X (NCERT 2025 ed.), Metals and Non-metals, p.47-48; Science, class X (NCERT 2025 ed.), Carbon and its Compounds, p.59; Physical Geography by PMF IAS, Thunderstorm, p.348

3. Acid-Base Reactions and Salt Formation (intermediate)

At its heart, an acid-base reaction is a chemical 'handshake' where the acidic H⁺ ions and the basic OH⁻ ions combine to form water (H₂O). This process is known as a neutralisation reaction. When an acid and a base react, they don't just disappear; they transform into water and a salt. For instance, the reaction between Hydrochloric acid and Sodium hydroxide produces common table salt (Sodium chloride) and water: NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l) Science, Class X (NCERT 2025 ed.), Chapter 2, p.21. While we often think of 'salt' as just what we put on food, in chemistry, a salt is any ionic compound formed during this process.

The nature of the resulting salt—whether it is acidic, basic, or neutral—depends entirely on the 'strength' of the parents (the acid and the base). Strength refers to how completely an acid or base dissociates into ions in water Science, Class X (NCERT 2025 ed.), Chapter 2, p.26. This 'tug-of-war' between the reactants determines the final pH of the salt solution:

Reactant Combination	Nature of Salt	pH Level
Strong Acid + Strong Base	Neutral	pH = 7
Strong Acid + Weak Base	Acidic	pH < 7
Weak Acid + Strong Base	Basic	pH > 7

Science, Class X (NCERT 2025 ed.), Chapter 2, p.29

Physically, salts are fascinating structures. They are not just random clumps of atoms but are organized into crystalline lattices held together by powerful electrostatic forces of attraction between oppositely charged ions. Because these ionic bonds are incredibly strong, salts possess high melting and boiling points; it takes a massive amount of thermal energy to break that lattice apart Science, Class X (NCERT 2025 ed.), Chapter 4, p.59. Furthermore, while solid salts are insulators because their ions are locked in place, they become excellent conductors of electricity when molten or dissolved in water, as the ions are finally free to move and carry a charge.

Sources: Science, Class X (NCERT 2025 ed.), Acids, Bases and Salts, p.21, 24, 26, 29; Science, Class X (NCERT 2025 ed.), Carbon and its Compounds, p.59

4. Electrolytes and Electrical Conductivity (intermediate)

To understand why some substances conduct electricity while others do not, we must look at the nature of charge carriers. In a metallic wire, electricity is the flow of electrons driven by a potential difference. However, in liquids and solutions, the story changes: the "messengers" of electric current are not free electrons, but ions—atoms or groups of atoms that have gained or lost electrons to become charged.

Ionic compounds, such as common salt (NaCl), are held together by powerful electrostatic forces of attraction in a rigid, crystalline lattice. In their solid state, these compounds are insulators because the ions are locked firmly in position and cannot move. However, when you melt these salts or dissolve them in water, the rigid structure breaks down. In the molten state, heat provides the energy to overcome these attractions; in an aqueous solution, water molecules pull the ions apart. Once freed, these ions can move toward electrodes when a voltage is applied, completing an electrical circuit Science, Metals and Non-metals, p.49.

It is important to distinguish between electrolytes (like acids, bases, and salts) and non-electrolytes. For example, while an aqueous solution of Hydrochloric acid (HCl) conducts electricity because it dissociates into H⁺ and Cl⁻ ions, solutions of compounds like glucose or alcohol do not conduct electricity. This is because glucose and alcohol are covalent compounds that do not form ions when dissolved in water Science, Acids, Bases and Salts, p.23, 25. Without mobile ions, there is no "vehicle" to carry the electric charge through the liquid.

Substance State	Conductivity	Reason
Solid Ionic Salt	Poor/None	Ions are fixed in a rigid lattice structure.
Molten/Aqueous Salt	Excellent	Electrostatic forces are overcome; ions move freely.
Glucose Solution	None	Covalent molecules do not dissociate into ions.

Sources: Science (NCERT 2025 ed.), Acids, Bases and Salts, p.23, 25; Science (NCERT 2025 ed.), Metals and Non-metals, p.49; Science (NCERT 2025 ed.), Carbon and its Compounds, p.59

5. Common Chemicals from Salts and Their Uses (basic)

To understand the chemicals derived from salts, we must first look at the nature of salts themselves. Salts are ionic compounds held together by powerful electrostatic forces of attraction between oppositely charged ions. This strong bonding creates an ordered crystalline lattice, which explains why salts generally have high melting and boiling points—it takes a massive amount of energy to break those bonds Science, Class X (NCERT 2025 ed.), Chapter 4, p. 59. While they are physically hard, they are also brittle; if you apply mechanical stress, like-charged ions align, repel each other, and the crystal shatters. Interestingly, while solid salts are insulators, they become excellent conductors of electricity when molten or dissolved in water because the ions are finally free to move and carry charge.

One of the most versatile starting points for industrial chemistry is Sodium Chloride (NaCl), or common salt. Through the electrolysis of its aqueous solution (brine), we obtain chlorine gas, which is the key ingredient for producing Bleaching Powder (Ca(ClO)₂). This is created by the action of chlorine on dry slaked lime [Ca(OH)₂] Science, Class X (NCERT 2025 ed.), Chapter 2, p. 30. Beyond the laundry room, bleaching powder acts as a potent oxidizing agent in chemical industries and is essential for making drinking water safe by killing germs Science, Class X (NCERT 2025 ed.), Chapter 2, p. 31.

Two other vital chemicals are Baking Soda (Sodium Hydrocarbonate) and Washing Soda (Sodium Carbonate). Baking soda is fascinating because its solubility is highly dependent on temperature—water at 70 °C can dissolve significantly more baking soda than water at 20 °C Science, Class VIII (NCERT 2025 ed.), Chapter 9, p. 138. When heated, baking soda decomposes, a reaction that is central to its use in cooking. On the other hand, Washing Soda serves a critical industrial role in softening hard water, ensuring that soaps can lather effectively Science, Class X (NCERT 2025 ed.), Chapter 2, p. 33.

Common Name	Chemical Formula	Primary Use
Bleaching Powder	Ca(ClO)₂	Disinfecting water; Textile bleaching
Baking Soda	NaHCO₃	Cooking; Antacids
Washing Soda	Na₂CO₃.10H₂O	Softening hard water; Glass manufacturing

Sources: Science, Class X (NCERT 2025 ed.), Carbon and its Compounds, p.59; Science, Class X (NCERT 2025 ed.), Acids, Bases and Salts, p.30-33; Science, Class VIII (NCERT 2025 ed.), The Amazing World of Solutes, Solvents, and Solutions, p.138

6. The Crystal Lattice Structure and Brittleness (intermediate)

When we look at a grain of common salt (NaCl), we aren't looking at a single molecule. In the world of chemistry, ionic compounds like salts exist as massive, three-dimensional structures known as crystal lattices. Instead of individual pairs of atoms, they are aggregates of millions of oppositely charged ions held together by powerful electrostatic forces of attraction Science, Metals and Non-metals, p.47. This lattice is highly ordered, with every positive ion (cation) surrounded by negative ions (anions), and vice versa, creating a very stable and hard solid Science, Metals and Non-metals, p.49.

This rigid internal architecture explains why salts have such high melting and boiling points. To melt a salt, you must provide enough thermal energy to overcome these intense inter-ionic attractions and break the lattice apart. For instance, Sodium Chloride (NaCl) requires temperatures as high as 1074 K (801°C) just to melt Science, Metals and Non-metals, p.48. Furthermore, because these ions are locked into fixed positions within the solid lattice, they cannot move to carry an electric current. However, once dissolved in water or melted into a liquid state, the lattice dissolves, the ions become mobile, and the substance becomes an excellent conductor of electricity Science, Metals and Non-metals, p.49.

One of the most distinctive features of this lattice is its brittleness. While metals can be hammered into sheets (malleability) because their atoms can slide past each other, ionic crystals shatter. When mechanical pressure is applied to a crystal, the layers of ions slide slightly. This shift can suddenly align ions of the same charge (positive next to positive, or negative next to negative). The resulting intense repulsive force between like charges causes the crystal to snap and break into pieces Science, Metals and Non-metals, p.49.

Sources: Science, Metals and Non-metals, p.47; Science, Metals and Non-metals, p.48; Science, Metals and Non-metals, p.49

7. Thermal Properties of Ionic Compounds (exam-level)

To understand the thermal behavior of ionic compounds, we must first look at their internal architecture. Ionic compounds are not just random clusters of atoms; they exist as a highly ordered three-dimensional crystalline lattice. In this structure, every positive ion (cation) is surrounded by negative ions (anions), and vice versa, held together by strong electrostatic forces of attraction. This "electrovalent bond" is incredibly robust, requiring a massive amount of external energy to disrupt Science, Metals and Non-metals, p.49.

Because of these intense forces, ionic compounds typically exhibit high melting and boiling points. For instance, common table salt (NaCl) melts at approximately 1074 K, and Calcium Oxide (CaO) requires a staggering 2850 K Science, Metals and Non-metals, p.48. This distinguishes them sharply from covalent carbon compounds, which generally have much lower melting points because the forces between their molecules are significantly weaker Science, Carbon and its Compounds, p.59.

The thermal energy we apply to a salt doesn't just increase its temperature; it eventually provides the kinetic energy needed to overcome the electrostatic pull. This leads to a fascinating change in electrical conductivity. In a solid state, ions are locked in a rigid structure and cannot move, making the solid salt a non-conductor. However, once the molten state is reached (or when dissolved in water), the lattice breaks down. The ions are freed to move toward opposite electrodes, allowing the substance to conduct electricity efficiently Science, Metals and Non-metals, p.49.

Finally, we must note their physical nature. While they are hard due to strong attraction, they are also brittle. If you apply mechanical stress, the layers of the crystal shift, potentially bringing ions of the same charge into alignment. These like-charges repel each other instantly, causing the crystal to shatter rather than deform Science, Metals and Non-metals, p.49.

State of Salt	Ion Mobility	Conductivity
Solid	Fixed in Lattice	Insulator (Non-conductor)
Molten (Liquid)	Free to move	Excellent Conductor
Aqueous (Solution)	Free to move	Excellent Conductor

Sources: Science, Metals and Non-metals, p.48; Science, Metals and Non-metals, p.49; Science, Carbon and its Compounds, p.58; Science, Carbon and its Compounds, p.59

8. Solving the Original PYQ (exam-level)

You’ve just explored the world of ionic bonding, and this question is the perfect test of how those microscopic forces manifest as macroscopic properties. The core concept here is the strong electrostatic force of attraction between oppositely charged ions (cations and anions). Because these bonds are incredibly strong and act in all directions, they pull ions into a highly ordered packing arrangement called a lattice (Option A). As you learned in Science, Class X (NCERT), this rigid structure is the fundamental reason why salts behave the way they do under heat and pressure.

To arrive at the correct answer, you must look for the logical inconsistency in the physical properties. Since the ionic lattice is so stable, it requires a tremendous amount of energy to break the bonds and change the state of the matter. Therefore, Option (B) is the correct answer because it falsely claims salts have low melting points. In reality, salts possess both high melting and high boiling points. This is a common UPSC tactic: pairing a true statement (high boiling point) with a false one (low melting point) to see if you are reading carefully or just skimming for familiar terms.

Finally, let’s look at the remaining properties to avoid common traps. Option (C) mentions that salts are brittle; this happens because mechanical stress shifts the lattice layers, bringing like-charged ions next to each other, leading to instant repulsion and shattering. Option (D) highlights a conditional property: salts are insulators as solids but conduct electricity in molten or aqueous states. UPSC often tests this nuance because it depends on ion mobility—the ions must be free to move to carry a charge. Recognizing these specific behaviors allows you to confidently eliminate the correct descriptions of salt to find the one false property.