1. There are works of art on the buletinboard at the back.

2. There are five works of art on the bulletinboard in the back.

3. There are many tables and chairs in the English classroom.

4. There is a computer in English Classroom 1.

5. There are two speakers on both sides on top in the room.

6. There are 10 windows on the walls of the room.

7. There are many brooms and dustpans in the broom cupboards.

8. There are works of tasks during the class on the bulletinboard at the back.

(Are they all grammatical? Would you correct any errors, please?)

bulletin board = always 2 words

I'm not sure about #5.

6. There are 10 windows in the room.

7. ... in the broom closet.

8. I don't understand "works of tasks" -- ??

1. There is a work of art on the bulletin board at the back.

2. There are five works of art on the bulletin board in the back.
3. There are many tables and chairs in the English classroom.
4. There is a computer in English Classroom 1.
5. There are two speakers on both sides on top of the room.
6. There are 10 windows on the walls of the room.
7. There are many brooms and dustpans in the broom cupboards.
8. There are tasks displayed on the bulletin board at the back during the class.

Note: I made some corrections to the sentences to improve their grammar and clarity. In a few cases, I adjusted the phrasing to sound more natural.