Introduction:
Seasoning of timber is a process of drying and reducing the moisture content in timber before it is used in construction. This process is essential to enhance the quality and performance of timber in construction applications. Among the given options, the correct answer is option 'B' which states that seasoning of timber increases its strength and durability. Let's delve into the details of how seasoning achieves this.

Enhancing Strength:
Seasoning helps in increasing the strength of timber in the following ways:

1. Reduction of Moisture Content: Green or freshly cut timber contains a high amount of moisture, which can range from 30% to 200% depending on the species. Seasoning removes this excess moisture from the timber, reducing its weight and making it stronger. The drying process allows the timber to reach equilibrium moisture content (EMC) with the surrounding environment, which typically ranges between 8% to 15% for construction purposes. This reduction in moisture content leads to improved strength properties of timber.

2. Minimization of Shrinkage and Swelling: Green timber tends to shrink and swell as it dries and absorbs moisture from the environment. Seasoning timber minimizes these dimensional changes and prevents warping, twisting, and cracking. By reducing the moisture content, seasoning stabilizes the timber and ensures that it retains its shape and size, enhancing its strength and structural integrity.

Improving Durability:
Seasoning also improves the durability of timber in the following ways:

1. Prevention of Decay and Pest Attacks: Freshly cut timber contains starches and sugars that serve as a food source for fungi, bacteria, and pests. Seasoning removes a significant portion of these organic substances, making the timber less susceptible to decay and insect attacks. This extends the lifespan of the timber in construction applications.

2. Enhancement of Chemical Treatment: Seasoned timber allows for better penetration and retention of preservatives and chemical treatments. These treatments protect the timber against wood-destroying organisms and increase its resistance to decay, rot, and insect infestations.

3. Improved Paint and Coating Adhesion: Seasoning helps in achieving better adhesion of paints, varnishes, and other coatings to the timber surface. This enhances the protective properties of the coatings and provides a more aesthetically pleasing finish.

Conclusion:
Seasoning of timber is a crucial step in the construction industry as it improves the strength and durability of timber. By reducing moisture content, seasoning enhances the strength properties of timber and minimizes dimensional changes. It also prevents decay, pest attacks, and improves the effectiveness of chemical treatments. Therefore, option 'B' is the correct answer that states seasoning increases the strength and durability of timber.