Fibre saturation point is a crucial factor to determine the properties of wood as it affects the strength, stiffness, and dimensional stability of wood. Let's understand the meaning and significance of fibre saturation point.

Meaning of Fibre Saturation Point:

Fibre saturation point (FSP) is defined as the moisture content at which the cell walls of wood are saturated with water, and the cell cavity contains no free water. In other words, it is the point where wood stops absorbing or releasing moisture from the environment, and the wood becomes dimensionally stable.

Significance of Fibre Saturation Point:

The significance of fibre saturation point lies in the fact that it affects the mechanical and physical properties of wood. Some of the important properties that are influenced by FSP are:

- Strength: The strength of wood is reduced when it is either too dry or too wet. At FSP, the wood has optimal moisture content, which provides maximum strength to wood.
- Stiffness: The stiffness of wood is also influenced by its moisture content. At FSP, the wood has maximum stiffness or modulus of elasticity (MOE).
- Dimensional Stability: Wood expands and contracts with changes in moisture content. At FSP, the wood has minimum dimensional changes, which makes it more stable and less prone to warping, twisting, or cracking.

Answer to the Question:

The correct answer to the question is option 'B,' i.e., when the cell walls are saturated with water, and the cell cavity contains no water. At this point, the wood has reached its maximum moisture content, and it is said to be at the fibre saturation point.

Option 'A' is incorrect because 12% moisture content is not the fibre saturation point. It is the equilibrium moisture content at which the wood neither gains nor loses moisture from the environment.

Option 'C' is incorrect because the cell walls are dried in this case, which means that the wood is below the fibre saturation point.

Option 'D' is also incorrect because the cell cavity contains no water in this case, which means that the wood is completely dry and has no moisture content.

Conclusion:

Fibre saturation point is a critical parameter that affects the properties of wood. It is the point at which the cell walls of wood are saturated with water, and the cell cavity contains no free water. At this point, the wood has optimal moisture content, which provides maximum strength, stiffness, and dimensional stability to wood.