The loosest type of coupling is data coupling. Data coupling is a type of coupling in which two modules communicate with each other by passing data. This is the loosest type of coupling because the modules are not dependent on each other’s internal implementation.
Control coupling is a type of coupling in which two modules communicate with each other by passing control information. This is a tighter type of coupling than data coupling because the modules are dependent on each other’s internal implementation.
External coupling is a type of coupling in which two modules communicate with each other through an external interface. This is the tightest type of coupling because the modules are completely dependent on each other’s internal implementation.
Pathological coupling is a type of coupling in which two modules communicate with each other in an arbitrary and unstructured way. This is the worst type of coupling because it makes it difficult to understand and maintain the code.
In conclusion, the loosest type of coupling is data coupling.