How can land that was formerly used as dumps, mines, or factory sites be.
rehabilitated?

clear out the junk, and plant some stuff

Explanation:

clear out all of the nasties, unless it is biodegradable, or you could get some mushrooms to break everything down, then you can go and plant some stuff or do whatever. You could turn it into a playground, park, whatever.

the answer is neither ball has a charge.

because if they were both positively charged, they will repel each other.

if they were positively and negatively charged, they will seek.