Q1: Dislocations are __________ defects.

ANS:B - line

Dislocations are line defects that occur within the crystal lattice structure of materials. These defects represent regions where the regular arrangement of atoms or ions in the crystal lattice is disrupted, leading to a deviation from the ideal crystal structure along a specific line or direction within the material. Here's a more detailed explanation:

1. Location within the lattice: Dislocations are localized defects that occur along lines or planes within the crystal lattice of a material. These lines are typically one-dimensional, extending through the material in specific directions.
2. Movement and deformation: Dislocations play a crucial role in the plastic deformation of materials. When an external force is applied to a material, dislocations can move through the crystal lattice, allowing atoms or ions to slip past one another. This movement of dislocations enables the material to deform plastically, changing its shape without fracturing.
3. Types of dislocations: There are different types of dislocations based on the arrangement of atoms or ions around the line defect. The most common types include edge dislocations, screw dislocations, and mixed dislocations. These dislocations differ in their atomic arrangements and how they move within the crystal lattice.
4. Effects on material properties: Dislocations can significantly influence the mechanical, electrical, and thermal properties of materials. For example, they can affect the strength, ductility, hardness, and conductivity of materials. The behavior of dislocations under various conditions also determines the material's response to external stresses, such as deformation, fracture, and fatigue.

In summary, dislocations are line defects that disrupt the regular arrangement of atoms or ions within the crystal lattice of materials. They play a fundamental role in the mechanical behavior and properties of materials, influencing their deformation mechanisms and response to external forces.