Explanation:

In the C programming language, storage class specifiers are used to define the scope, visibility, and lifetime of variables. There are four storage class specifiers in C: `auto`, `register`, `static`, and `extern`.

1. `volatile`:
The `volatile` storage class specifier is not a part of the list of storage class specifiers in C. Instead, `volatile` is a type qualifier that indicates that a variable's value can be changed unexpectedly by external factors, such as hardware or interrupts. It tells the compiler not to optimize the variable and always read from or write to it in memory.

2. `extern`:
The `extern` storage class specifier is used to declare a variable that is defined in another source file or library. It is used to provide a declaration without allocating storage space for the variable. The actual definition of the variable is located in another file, and the `extern` declaration allows the program to access it.

3. `typedef`:
The `typedef` storage class specifier is used to create a new name for an existing data type. It allows the programmer to create aliases or alternative names for types already defined. It is commonly used to make code more readable and maintainable.

4. `static`:
The `static` storage class specifier is used to declare variables that are local to a block, function, or file. When a variable is declared as `static`, it retains its value between function calls and has a lifetime equal to the entire duration of the program. Additionally, `static` variables are only visible within the scope they are defined in, making them useful for maintaining state information.

Therefore, the correct answer is option 'A', `volatile`, as it is not a storage class specifier but a type qualifier in C.