The correct answer to the question “Which of the following is not a valid data type in C language” is option ©. Long. As rest of the options like char, float, and double are valid data types in C Language, except long. If you are wishing to learn C, check out the C tutorial, and if you want to get certified, then enroll in the C Language course from Intellipaat. Also, as a starter, watch the following video on, C Tutorial for Beginners from our experts.