Praseodymium is a lanthanide metal with symbol Pr and an approximate molar mass of 140 grams per mole. When a 420 milligram sample of praseodymium metal is burned in an oxygen rich atmosphere, it is converted completely into a mixed praseodymium oxide and its mass increases by 88 milligrams. Answer the following two questions about this compound: 1) What is the formula unit of this compound? 2) All the praseodymium in this oxide is in either the +3 or +4 oxidation state. How many praseodymium atoms per formula unit are in the +4 oxidation state?