The correct answer is: None of the above.
In programming, an identifier is a name that is used to refer to a variable, function, class, or other entity. Identifiers are case-sensitive, so “name” and “Names” are different identifiers. Identifiers must also start with a letter or underscore, and can only contain letters, numbers, and underscores.
In the options given, only “identifier 1” and “identifier_2” are both identifiers that start with a letter and contain only letters, numbers, and underscores. However, they are not considered to be identical because they are case-sensitive.
The other options are not identifiers because they do not start with a letter or underscore, or they contain characters that are not letters, numbers, or underscores.