The phrase "en la mesa hay mucho libros" is incorrect. It should be "en la mesa hay muchos libros" to match the plural form of "libros."
"Hay en la clase" means "There is in the class" in English.
Sí, hay cuadernos en la clase. (Yes, there are notebooks in the class.)
Sí, hay estudiantes de México en la clase.
Hay veinte estudiantes en la clase de español.
Hay muches alumnos en la clase means There are many students/pupils in the class
"¿Qué hay en clase?" translates to "What is there in class?" It is a question asking about the things or activities that are present or occurring in a classroom.
what is in that class
It means there are books in the library.
"Is there a computer in your class?"
The litteral translation is - There are students in the class Mexico
How many female students are in your classroom and how many male students are there and is there a female or male teacher in your classroom and how many desks are in your classroom.