You are standing in a lift. The force on the floor of the lift due to your weight will

The correct choice is: “become zero when the lift moves down with an acceleration of 9.8 m/s²”

The force you exert on the floor equals the normal reaction R. For a lift accelerating downwards with acceleration a: mg − R = ma, so R = m(g − a). When a = g = 9.8 m/s², R = 0: you and the lift fall freely together and you feel weightless.

For a lift accelerating upwards, R = m(g + a), which becomes 2mg when a = g, not zero. So the force does not become zero for acceleration “in any direction”, and it does not “remain unchanged” either, because it depends on the lift's acceleration.