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.
Krypton was discovered on May 30, 1898 by Sir William Ramsay, a Scottish chemist, and Morris M. Travers, an English chemist, while studying liquefied air. Small amounts of liquid krypton remained behind after the more volatile components of liquid air had boiled away. The earth's atmosphere is about 0.0001% krypton. The high cost of obtaining krypton from the air has limited its practical applications. Krypton is used in some types of photographic flashes used in high speed photography. Some fluorescent light bulbs are filled with a mixture of krypton and argon gases. Krypton gas is also combined with other gases to make luminous signs that glow with a greenish-yellow light. In 1960, the length of the meter was defined in terms of the orange-red spectral line of krypton-86, an isotope of krypton. Once thought to be completely inert, krypton is known to form a few compounds.