Answer: A. Centre of pressure
The hydrostatic force acts through centre of pressure.
Hydrostatic pressure is the pressure acting on a stationary body in the stationary fluid. Hydrostatic pressure at a distance of “h” from the free surface of the water level can be expressed as ρgh.
where, ρ= density of fluid, g= acceleration due to gravity, and h is the height of fluid above the body from the free surface.
Hydrostatic pressure acts on the centre of pressure which can be expressed as
where, I= moment of inertia about free surface
Ig=moment of inertia about centre of gravity of body. Hence, the hydrostatic force acts through centre of pressure.
NOTE: The metacentre is the point through which the centre of buoyancy line passes.