1. There are a desk, a char and a chalkboard in the classroom.
2. There are desk, char and chalkboard in the classroom.
3. There is a chair, a desk, and a chalkboard in the classroom.
1. There are a desk, a chair and a chalkboard in the classroom.
2. There are desk, chair and chalkboard in the classroom.
3. There is a chair, a desk, and a chalkboard in the classroom.
The simple answer is that only #1 is correct. It is possible to dream up situations in which #2 and #3 might be uttered, but there is little point.