Which of the following is a valid variable name in Python?

• A. 1st_variable
• B. my_variable
• C. my-variable
• D. my variable

Answer: (B)

In Python, a valid variable name must adhere to specific rules. It can include letters (both uppercase and lowercase), digits, and underscores, but it cannot start with a digit. Additionally, variable names cannot contain spaces or special characters like hyphens.

The choice that meets all these criteria is my_variable. It starts with a letter, contains only letters and an underscore, and does not have spaces or special characters, making it a completely valid identifier in Python.

In contrast, the other options violate one or more of these naming conventions. For example, 1st_variable starts with a digit, which is not permitted. The name my-variable includes a hyphen, which Python interprets as a subtraction operator. Similarly, my variable contains a space, which is also not allowed. Therefore, my_variable is the only one that qualifies as a valid variable name.