Q : how is the weight of the body in a freely falling lift zero?

A body in free fall (which by definition entails no aerodynamic forces) near the surface of the earth has an acceleration approximately equal to 9.8 m s⁻²with respect to a coordinate frame tied to the earth. If the body is in a freely falling lift and subject to no pushes or pulls from the lift or its contents, the acceleration with respect to the lift would be zero. Therefore, the weight of a body in a freely falling lift would be zero.