Why cesium is more electron positive than francium?

Caesium is more reactive. Generally as you go down the periodic table, electro-positivity increases. However, for the really heavy elements, the presence of so many positively charged protons in the nucleus has the affect of causing the electrons to move round at incredibly fast speeds approaching the speed of light. As Einstein realised at such speeds strange things begin to happen. The electrons become a little closer to the nucleus than expected and they also become slightly harder to remove than expected.
The electrons then become a little closer to the nucleus than expected and they also become slightly harder to remove than expected. Hence as a result we see that cesium is morereactive than francium. Cs have large atomic size so it easily donateelectrons. So it most reactive metal in Lithium family
Thus Caesium is more electropositive(reactive) than Francium