Explanation:

Conduction:
Conduction is the process of heat transfer through direct contact between particles of a substance. It occurs when there is a difference in temperature between two objects or regions, causing the heat to flow from the higher temperature region to the lower temperature region. In solids, conduction takes place through the vibration and collision of atoms or molecules.

Conduction in Gases:
Gases have loosely packed particles that are constantly moving and have a high amount of empty space between them. Due to this, the transfer of heat through conduction in gases is negligible. The particles in gases are not closely packed, and there is a lack of strong intermolecular forces that can transfer heat effectively. Therefore, conduction does not occur significantly in gases.

Conduction in Liquids:
In liquids, conduction takes place to some extent. The particles in liquids are closer together compared to gases, allowing for better heat transfer. However, the movement of particles in liquids is not as ordered as in solids. The heat transfer through conduction in liquids is slower compared to solids but faster than gases.

Conduction in Solids:
Solids are excellent conductors of heat because the particles are closely packed, and they have strong intermolecular forces. When heat is applied to one end of a solid, the particles in that region gain kinetic energy and vibrate, transferring the energy to adjacent particles through collisions. This process continues, transferring heat energy from one end to the other. The tightly packed particles and strong intermolecular forces in solids allow for efficient conduction of heat.

Conclusion:
Conduction occurs in solids due to the close proximity of particles and strong intermolecular forces. Gases and liquids are poor conductors of heat because their particles are not closely packed, and the intermolecular forces are weaker. Therefore, the correct answer is option 'B' - conduction takes place in solids only.