This question likely has a set of choices. In the absent of it, I can answer it using the second law of thermodynamic.
The second law of thermodinamy states that an isolated system the entropy will increase.
Entropy is a measure of the diosrder of the molecules of system.
Then in an isolated system statistical odds predict that molecules will be as mixed (disordered) as they can.
As an example, you can imagin that you add a drop of blue coloarant to a glass of water. If the system will be in pertect order the blue color will remain in a fixed place in the water. But, the reality, and prediction of theory, is that the molecules of the colorant will spread as much as they can and that is the reason why the whole water will be coloured in blue.