The resultant of all normal pressures acts

In fluid mechanics, the center of pressure is the point where the total hydrostatic force on a submerged surface can be considered to act. This concept is crucial for understanding the distribution of pressure forces on submerged surfaces. When a body is submerged in a fluid, such as water, the fluid exerts pressure on the surface of the body. This pressure varies across the surface depending on factors like depth and orientation.

The center of pressure is the point through which the resultant of all these pressure forces can be assumed to act. It's important to note that the center of pressure may not necessarily coincide with the centroid or center of gravity of the submerged surface. Instead, it depends on the shape and orientation of the surface and the distribution of pressure on it.

Therefore, in the context of the question, the correct answer is Option B: "At center of pressure." This is because the resultant of all normal pressures in a fluid acts at the center of pressure, representing the combined effect of pressure forces on the submerged surface.