Which of the following is not a legal identifier? A. age C. 9th Class B. $Amount D. nullValue
The Correct Answer and Explanation is:
The correct answer is B. 9th Class.
In programming, a legal identifier is a name used to identify variables, functions, classes, or other entities in the code. These identifiers must follow certain rules, which can vary slightly between different programming languages. However, most languages (like Java, Python, C++, etc.) share common conventions when it comes to legal identifiers.
Explanation:
- A. age:
This is a legal identifier. It starts with a letter, which is required by most programming languages, and it doesn’t contain any illegal characters like spaces or special symbols. It’s a valid variable name in languages like Python, Java, and JavaScript. - B. 9th Class:
This is not a legal identifier. Identifiers cannot begin with a digit (like “9”). In this case, the identifier begins with the digit “9”, which violates the rules of most programming languages. Additionally, spaces are generally not allowed in identifiers, and here we have a space between “9th” and “Class.” This further invalidates it as an identifier. - C. $Amount:
This is a legal identifier. In many programming languages, including JavaScript and Python, the dollar sign ($) is considered a valid character for variable names. In fact, it’s frequently used in certain contexts (like denoting special variables in JavaScript or jQuery). Therefore,$Amountis a valid identifier. - D. (unspecified in your question):
Since “D” is not specified in your question, I can’t analyze it here. But if it were an identifier that broke any naming conventions, such as using spaces or starting with a number, it would also be invalid.
Key Rules for Identifiers:
- Start with a letter or an underscore (
_), not a number. - Use only letters, digits, and underscores. No special characters like spaces, punctuation marks, or symbols (except for
_and$in some languages). - Avoid using reserved keywords (like
int,return,class, etc.).
So, “9th Class” is not a legal identifier because it violates two important rules: it starts with a number, and it contains a space.
