Polonium is a radioactive metal that is used as a heat source in space satellites. polonium has a simple cubic unit cell. how many atoms of po are present in each unit cell?

You're probably talking about the cubic crystal structure of alpha polonium, the only element known to exist that way. Each alpha polonium crystal has 27 atoms in a three by three arrangement. Alpha polonium is an allotrope of the element polonium. Allotropes are physical forms of a single element. An example is carbon, which exists as diamond and graphite.