Answer: Because the acre is a measure of area, it has no definite perimeter. For example, using the examples in question one, the perimeter of the long, skinny sidewalk acre would be 17,434 feet (more than 3 miles), but the perimeter of the square acre would be 835 feet.
No other molecular fluoride of krypton has been isolated, so all krypton compounds are derived from KrF 2, where Kr is in the +2 oxidation state. Krypton difluoride is a powerful oxidative fluorinating agent. (Its oxidizing power means that it extracts electrons from other substances and confers on them a positive charge.
Kryptonite is a material from the Superman mythos, specifically the ore form of a radioactive element from Superman's home planet of Krypton.