Why finger print is the cheapest and easiest method of personal identification?​

Well fingerprint are more versatile and easy to acquire than any other biometrics. They are accepted in a court of law and no two people (not even identical twins) have the same fingerprints, it is extremely easy for even the most accomplished criminals to leave incriminating fingerprints at the scene of a crime. Fingerprints are one of a kind.

Because a model would make the investigation easier to understand

Spontaneity tell us the direction of the reaction, but not how fast it goes. gibbs free energy brings together enthalpy, entropy and temperature in one easy formula. g = h - ts. and, finally the sign of delta g is always negative for a spontaneous reaction.