Thanks for your comment . Do you think I will be fine if I go in Upssala with 5000 SEK month including all cost house , food , internet , party , transports ? <| sep |> xing is platinum or higher i believe <| sep |> I almost never saw a janna flame . Probably because there are no jannas in my games . <| sep |> Lead 0 is metallic lead . It has not lost any electrons from its valence electrons . Lead sits under carbon so it has four valence electrons . If it loses 2 and becomes lead II Pb 2 it has a filled s shell which is stable . Lead can further oxidize to lead IV Pb 4 making it isoelectronic with a noble gas . In the perovskite structure formula ABX 3 , when X is a halogen , A and B must total to a 3 . Since A is usually an alkali metal or small organic cation 1 that means B must be 2 . Therefore the perovskite with lead methylammonium lead iodide specifically contains lead II . Tin can also be used in these structure because tin and lead are in the same group and make the same ions . What they fail to mention in the article is that the tin perovskite is not oxygen stable tin II oxidizes in air rapidly to tin IV and therefore these cells must be made under oxygen free conditions and then will have to be sealed from oxygen . Lead doesn ' t have this problem because the lead atoms nucleus is so large it ' s core electrons are moving at relativistic speeds which causes the s orbitals to contract and lower in energy which stabilizes the s electrons from oxidation . Edit grammar fixSource I work in a lab that studies these materials