We study the emission of fragments in central collisions of light and heavily charged systems of 40Ar+45Sc and 84Kr+l97Au,respectively,using the Quantum Molecular Dynamics(QMD)model as the primary mod-el.The fragments are identified using an energy based clusterization algorithm,i.e.,the Simulated Annealing Clus-terization Algorithm(SACA).The charge distributions of intermediate mass fragments[3≤Zf≤ 12]are fiitted with power-law(∝ Zfτ)and exponential(∝ e-λZf)fits in order to extract the parameters r and λ,whose minimum values are also sometimes linked with the onset of fragmentation or the critical point for a liquid-gas phase transition.Oth-er parameters such as the normalized second moment 〈S2 〉,〈y2〉,average size of the second largest cluster〈 Zmax2 〉,phase separation parameter(Sp),bimodal parameter(P),information entropy(H),and Zipfs law are also analyzed to find the exact energy of the onset of fragmentation.Our detailed analysis predicts that an energy point exists between 20-23.1 MeV/nucleon,which is very close to the experimentally observed value of 23.9 MeV/nucle-on for the40Ar+45Sc reaction.We also find that the critical energy deduced using Zipfs law is higher than those pre-dicted from other critical exponents.Moreover,no minimum is found for r values of the highly charged system ofrn 84Kr+197Au,in agreement with experimental findings and various theoretical calculations.We observe that the QMD+SACA model calculations are in agreement with the experimental observations.This agreement supports our res-ults regarding the energy point of the liquid-gas phase transition and the onset of fragmentation.