Generally, the more empty the outer electron shell, the more reactive the element. Helium has two(2) electrons, and is thus full, all the other noble elements has eight(8) electrons in it's outer electron shell, so they are also full. *And for everyone's sake, krypton is not green, but colorless, and forms white crystals when solid.
(a) Jubilees was written between 153 B.C. and the year of Hyrcanus' breach with the Pharisees. (1) It was written during the pontificate of the Maccabean family, and not earlier than 155 B.C., when this office was assumed by Jonathan the Maccabee.
The Lord told Moses to begin counting sabbath years and the jubilee cycle when they entered the promised land (Lev. 25), which suggests beginning the count immediately at that time. The jubilee is the fiftieth year after the cycle begins, but the cycle only has seven sets of seven years, or 49 years. Thus, the 50th year of the cycle is the same as the first year of the cycle. That and several other events indicate that they indeed entered the promised land in a jubilee year. The year 2009 marks 70 sets of 49-year jubilee cycles since 1422 BC.