The resultant upward pressure of the fluid on an immersed body due to its tendency to uplift the sub-merged body is called A. upthrust B. reaction C. buoyancy D. metacentre

The correct answer is A. upthrust.

Upthrust is the upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. It is also known as buoyancy.

Reaction is the force that is exerted in the opposite direction to the force that is applied.

Metacentre is the point of intersection of the vertical lines through the centre of buoyancy and the centre of gravity of a floating body.

Upthrust is the only force that acts in the upward direction on an immersed body. The other three forces act in the downward direction.