Solids have definite shapes and volumes. Which explanation best describes why, in terms of intermolecular forces inside a solid?

Introduction / Context:
One of the basic differences between solids, liquids and gases is that solids have definite shapes and volumes, whereas liquids take the shape of their container and gases fill all available space. From a microscopic point of view, this behaviour is explained in terms of intermolecular forces. This question asks you to identify which type of force and what relative magnitude of that force is responsible for the definite shape of solids.

Given Data / Assumptions:

• We compare cohesion (attraction between like molecules) and adhesion (attraction between unlike molecules).
• We consider the internal structure of a typical crystalline or amorphous solid.
• Temperature is assumed low enough that the material remains in the solid state.
• We ignore external forces such as gravity except as they affect the macroscopic shape.

Concept / Approach:
In solids, molecules or atoms are packed closely together in a fixed arrangement. Strong cohesive forces between neighbouring particles hold them in place, allowing only small vibrations about fixed positions. Because of these strong cohesion forces, the particles do not move freely past one another, and the solid maintains a definite shape and volume. In liquids, cohesion is weaker, so molecules can slide around while remaining close, and in gases, cohesion is negligible, so particles move freely. Adhesion describes how solids and liquids stick to other materials, but it does not primarily determine the shape of the solid itself.

Step-by-Step Solution:
Step 1: Recall that cohesion refers to attractive forces between molecules of the same substance. Step 2: In a solid, particles are closely packed in a regular or semi regular arrangement. Step 3: Strong cohesive forces keep each particle near its equilibrium position, allowing little relative motion. Step 4: Because the particles cannot easily move past one another, the solid retains a definite shape and volume. Step 5: Adhesion involves attraction between different materials, such as glass and water, and affects wetting and sticking but not the basic solid shape. Step 6: Therefore, the best explanation is that the forces of cohesion are very large in solids.

Verification / Alternative check:
Everyday experience supports this reasoning. Ice cubes, metal blocks and wooden pieces all retain their shapes even when moved from one container to another, showing that internal structure holds them together. When a solid is heated strongly enough to melt, its internal cohesive forces are partially overcome, and it becomes a liquid that flows and takes the shape of its container. This change confirms that the key difference lies in how strongly the particles are bound together by cohesive forces.

Why Other Options Are Wrong:
Because the forces of cohesion are very small: If cohesion were small, particles would move freely and the material would behave like a liquid or gas, not a solid.

Because the forces of adhesion are very large: Adhesion describes interactions with other materials and is more relevant to phenomena like wetting; it does not explain the internal rigidity of a solid.

Because the forces of adhesion are very small: This says little about the internal structure of the solid and does not account for its definite shape.

Common Pitfalls:
A common mistake is to confuse cohesion and adhesion. Students may recall that water droplets form due to cohesion and that water sticks to glass due to adhesion, but they do not always connect cohesion to the rigidity of solids. Another error is to think that solids are hard simply because particles are closer together, without considering the strength of the attractive forces holding them in place. Remember that closeness plus strong cohesive forces together give solids their definite shape.

Final Answer:
Solids have definite shapes mainly because the forces of cohesion between their molecules are very large.