What are the postulates of VBT and why is sigma bond stronger that pi bond ?

@ ankit 
in sigma bond , electron cloud is present close to the nucleaus , so, it is less reactive , more stable and strong . 
the electron cloud in case of pi bond , is scattered above and below the nuclei , so, it can easily react , hence , less strong as compared to sigma bond . 
i am enlisting some of the postulates of vbt here 
1- the atomic orbitals of two atoms overlap each other to form a bond , greater the overlapping , stronger will be the bond . 
2- at the equilibrium , the internuclear distance , the energy touches a minimum , any attempt to bring the nuclei still closer result in sudden increase IN energy . 
3- beacuse of orbital overlap electron density increase between the nuclei . 
4- the direction of covalent bond , is along the region of overlap of atomic orbital . 
5- sigma bond forms due to head on head overlapping along internuclear axis . 
HOPE IT CLEARS YOUR DOUBT 
ALL THE BEST ..