If the neuron is stimulated such that its membrane potential changes to 50 mV, what is the sign of the driving force for Cl- ions and in which direction will these ions move across the membrane?

in simple terms, the principle states that the buoyancy force on an object is equal to the weight of the fluid displaced by the object, or the density of the fluid multiplied by the submerged volume times the gravitational acceleration, g. this is also known as upthrust.