Question 2
Why does an upthrust arise on an object immersed in water?
The right answer is the one marked above.
The lower face is deeper, so the pressure on it is greater. The upward force on the lower face therefore exceeds the downward force on the upper face, and the difference acts upwards.
The two faces of a cube have equal areas — only the pressure differs. And the object's weight does not fall in water; what falls is the apparent weight, which is a consequence of the upthrust, not its cause.