The Question is from neet-chemistry the-solid-state , and it was created by the author THIRUPATHI REDDY

Question

A crystalline solid is hard, brittle, has a high melting point, and conducts electricity only in the molten state.  Which type of solid is it most likely to be?

THIRUPATHI REDDY · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
 **Primary Concept**: Properties of different types of solids
 **Related Topics**: Chemical bonding, crystal structures
 **Prerequisites**: Understanding of ionic bonds, metallic bonds, covalent bonds, and intermolecular forces.
## SOLUTION PATHWAY
**Given Information**:
The solid is crystalline, hard, brittle, has a high melting point, and conducts electricity only when molten.
**Method & Steps**:
1. Analyze the properties:
  Reasoning:  The properties given suggest strong electrostatic forces holding the solid together.  The high melting point indicates strong bonds requiring significant energy to break.  The brittleness suggests a rigid structure that easily fractures when stress is applied. The electrical conductivity only in the molten state implies that charge carriers (ions) are immobile in the solid state but mobile when the solid melts.
  Formula/Rule: None directly applicable, but understanding of bonding types is crucial.
2. Consider the types of solids:
  Working: Let's examine each option:
  	* **Ionic solids:** These are formed by electrostatic attraction between oppositely charged ions. They are typically hard, brittle, have high melting points, and conduct electricity when molten (ions become mobile) or in solution. 
  	* **Metallic solids:**  These are formed by a sea of delocalized electrons surrounding metal cations.  They are usually malleable, ductile, and conduct electricity in both solid and molten states.
  	* **Molecular solids:** These are formed by weak intermolecular forces (like van der Waals forces, hydrogen bonds). They are typically soft, have low melting points, and are poor conductors of electricity.
  	* **Covalent network solids:** These are formed by a continuous network of covalent bonds (like diamond or silicon dioxide). They are very hard, have very high melting points, and are generally poor conductors of electricity.
  Key Point: The key here is the combination of high melting point, brittleness, and conductivity only in the molten state.
3. Determine the most likely solid type:
  Result: Ionic solids best fit the given description.
  Verification: All properties of the solid align with the characteristics of ionic solids.
 ## OPTION ANALYSIS
A ✓: Ionic solids have strong electrostatic attractions between ions, leading to hardness, brittleness, and high melting points.  The ions are immobile in the solid state, preventing electrical conductivity.  However, in the molten state, ions are free to move, allowing for electrical conductivity.
B :x: Metallic solids are usually malleable and ductile, not brittle, and conduct electricity in both solid and molten states.
C :x: Molecular solids are soft, have low melting points, and are poor conductors of electricity.
D :x: Covalent network solids are very hard and have extremely high melting points but are typically poor conductors of electricity (except for graphite, which is an exception).
 ## LEARNING AIDS
 **Common Mistakes**:
  1. Confusing ionic solids with metallic solids:  Remember that metallic solids are good conductors in both solid and liquid states, while ionic solids conduct only when molten or dissolved.
  2. Overlooking the significance of brittleness: Brittleness is a key indicator of ionic solids due to the rigid structure and the disruption of electrostatic forces upon stress.
 **Quick Tips**:
  1.  If a solid is hard, brittle, has a high melting point, and conducts electricity only when molten, it's almost certainly an ionic solid.
  2. Use a mnemonic device:  Think “HIBC” – Hard, Brittle, High melting point, Conducts (only when molten) for Ionic solids.

THIRUPATHI REDDY · Answer

The correct Option is "Ionic solid"

THIRUPATHI REDDY · Answer

Metallic solid

THIRUPATHI REDDY · Answer

Molecular solid

THIRUPATHI REDDY · Answer

Covalent network solid

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