Final answer:
The default values for data fields in programming languages are false for a boolean type, 0 for a numeric type, and null for an object type.
Step-by-step explanation:
The default value for a data field of a boolean type is false, for a numeric type it is 0 (zero), and for an object type it is null. In programming, specifically within the context of object-oriented languages like Java and C#, these default values are automatically assigned to fields of a class when an instance of the class is created and no explicit initializations are provided.