Solution:

Assertion (A) is true: As the magnet falls, eddy currents are induced in the copper tube. By Lenz's law, these currents create a magnetic field that produces an upward braking force opposing the magnet's motion. This opposing force increases with the magnet's speed, thus reducing the net downward force and acceleration. Reason (R) is true: As the magnet falls downwards, the induced magnetic force always opposes the motion, meaning its direction is always upwards. However, (R) does not explain the *decrease* in acceleration, which is due to the *increasing magnitude* of the opposing force with speed. So, (R) is not the correct explanation of (A).