Rate of a general reaction A + B  $\to$ Products can be expressed as follows on the basis of collision theory Rate =  $Z_{AB}{e}^{-Ea/RT}$.  Which of the following statement is not correct for the above expression? 

Z is collision frequency and is equal to number of collisions per second per unit volume of the reaction mixture.

$e^{-Ea/RT}$ is the fraction of molecules with kinetic energy equal to or greater than E_a
 

All the molecules which collide with one other are effective collisions.

E_a is activation energy of the reaction.