A scale will read a force value that is equal to the normal force exerted by the scale upon the object that is in contact with its top surface. By analyzing all the other forces that act upon that object, it is possible to predict a value for the scale reading.
 

The 5.0-kg box and the scale are both falling. The a = 9.8 m/s² is the indicator that the two objects are in free-fall. They are falling at the same rate as is expected for free-falling objects. 

Normal forces exist when two in-contact objects have their surfaces pressed together. For instance, if you sit on a chair cushion, gravity pulls you downwards and your body and the chair cushion are pressed together. This pressing together of the two surfaces causes the normal force. But if the chair happened to be falling, as it sometimes does at an amusement partk, then it is unable to push upwards. The surfaces of two side-by-side  free-falling objects cannot push upon each other. The result is that there is no normal force. 

This is the type of thinking you need to apply to this question. Now go answer it with confidence.