To answer this question, you need to understand the concept of keywords and reserved words in Java.
Keywords and reserved words in Java are words that have a predefined meaning and cannot be used as identifiers (such as variable names or method names). These words are part of the Java language syntax and are reserved for specific purposes.
Let's go through each option to understand why it is correct or incorrect:
Option A) if - This option is incorrect because "if" is a keyword in Java used for conditional statements.
Option B) then - This option is correct because "then" is not a keyword or reserved word in Java. It is commonly used in other programming languages like Pascal, but not in Java.
Option C) goto - This option is incorrect because "goto" is a reserved word in Java, although it is not used in the language. It was reserved for future use but was never implemented.
Option D) while - This option is incorrect because "while" is a keyword in Java used for loop statements.
Option E) case - This option is incorrect because "case" is a keyword in Java used in switch statements.
The correct answer is B) then. This option is correct because "then" is not a keyword or reserved word in Java.