Which property of air makes it effective in protecting firefighters?

this would be your  Air is a good insulator and doesn’t conduct heat very well. This property of air makes it effective in protecting firefighters from burns.

Explanation:

let me be

probably not if net force is zero

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.