Câu 4 : 

$XO_2 \to$ X có hóa trị IV

$H_2Y \to$ Y có hóa trị II

Theo quy tắc hóa trị, CTHH tạo bởi X và Y là $XY_2$

Câu 5 : 

$X_2O_3 \to$ X có hóa trị III

$HY \to$ Y có hóa trị I

Theo quy tắc hóa trị, CTHH tạo bởi X và Y là $XY_3$

1. 2Ca + O₂ \(\underrightarrow{t^o}\) 2CaO ( 2:1:2 )

2. 4Na + O₂ \(\underrightarrow{t^o}\) 2Na₂O ( 4:1:2 )

3. 4Al + 3O₂ \(\underrightarrow{t^o}\) 2Al₂O₃ ( 4:3:2 )

4. 4P + 5O₂ \(\underrightarrow{t^o}\) 2P₂O₅ ( 4:2:5 )

5. 3Fe + 2O₂ \(\underrightarrow{t^o}\) Fe₃O₄ ( 3:2:1 )

6. 2KClO₃ \(\underrightarrow{t^o}\) 2KCl + 3O₂ ( 2:2:3 )

7. Zn + 2HCl \(\rightarrow\) ZnCl₂ + H₂ ( 1:2:1:1 )

8. 2Al + 6HCl \(\rightarrow\) 2AlCl₃ + 3H₂ ( 2:6:2:3 )

9. Fe + H₂SO₄ \(\rightarrow\) FeSO₄ + H₂ (1:1:1:1 )

10. 2Al + 3H₂SO₄ \(\rightarrow\) Al₂(SO₄)₃ + 3H₂ ( 2:3:1:3 )

1. If you are calm, you won't make a wrong decision.
2. These wonderful poems were written by a great poet.
3.Because of rained heavily, Jane didn't go fishing yesterday.
4.Vietnamese people use Khue Van pavilion as a symbol of Hanoi.
5. His idea is not the same as me.
6. Those modern paintings are not as expensive as these Dong Ho paintings.
7. What food do you like?
8.These machines are used by chefs to mix the ingredients.
9. It i've most seen such a boring movie.
10. There are not many eggs in the fridge.
11.They started living there 2 years ago.
12. I have never drunk cocktail before.
13.This exercise is not as difficult as the last one.
14. I find playing computer games boring.
15. The new building has the same height as the old one.
16. She didn't have enough eggs to make an omelette.
17. In spite of promising that wouldn't be late, he didn't arrive until 9 o'clock.
18. 

18. were enjoying 

19. gave

20. was bleeding

21. went

1 B

2 B

3 A

4 D

5 A

6 C

7 D

8 D

9 A

10 C

11 B

12 C

13 B

14 B

15 B

16 D

17 C

18 A

19 B

20 B

III

1 C

2 A

3 C

4 D

5 D

6 B

7 D

8 B

9 D

10 A

11 B