These are the Most Expensive Elements on Earth.
Francium
It costs $1 billion per gram. Because The half-life of this element is about 22 minutes, which means any viewable quantity of the element would immediately vaporize. But it is assumed that francium would appear as a highly reactive metal.
Californium
It costs $25-27 million per gram.This element was first developed in 1950 at the University of California Radiation Laboratory, by bombarding curium with alpha particles.
