Which of the following statements is incorrect about the Categories in Objective C?

It is used to add functionality to the existing class without inheriting that class.

It is mandatory to have the implementation of the code to specify category in the class.

@interface ClassName (CategoryName) @end is the correct syntax to declare a category.

The methods in a category have access to all instances of the class and also the subclass.

A category is usually declared in a separate header file and implemented in a separate source code file.