The correct answer is option 'A': Yes.

Explanation:
In an ordinary bolt, the effect of the impulsive loads applied axially is indeed concentrated on the cross-sectional area at the root of the threads. This is due to the design of the bolt and the way it transfers the load.

When a bolt is tightened, the threads of the bolt engage with the corresponding threads in the nut or the threaded hole. As the bolt is tightened, the threads apply a clamping force on the connected parts, creating a joint.

The impulsive loads applied axially on the bolt refer to the external forces or shocks that act in the same line as the bolt's axis. These loads can be caused by various factors such as vibrations, impacts, or sudden changes in the load.

Since the bolt is designed to transfer the load through the engagement of threads, the cross-sectional area at the root of the threads experiences the highest stress concentration. This is because the threads act as a wedge, concentrating the load onto a smaller area.

By concentrating the load on the cross-sectional area at the root of the threads, the bolt can effectively transfer the applied impulsive loads to the connected parts. This ensures that the joint remains secure and prevents the bolt from loosening or failing under the applied loads.

It is important to note that the design and material of the bolt play a crucial role in determining its strength and ability to withstand the impulsive loads. Bolts are typically made from high-strength materials such as steel and undergo specific heat treatment processes to enhance their mechanical properties.

In summary, the effect of impulsive loads applied axially on an ordinary bolt is concentrated on the cross-sectional area at the root of the threads. This design allows the bolt to effectively transfer the applied loads and maintain the integrity of the joint.