Thực hiện phản ứng este hóa 23 gam C2 H5 OH với CH3 COOH dư, với hiệu suất phản ứng đạt 55%. Khối lượng CH3 COOC2 H5 tạo thành là A: 19,8 gam. B: 44 gam. C: 12,65 gam. D: 24,2 gam.

Em hãy giải thích rõ diễn biến tâm trạng của người anh khi đứng trước bức tranh của em gái:ngỡ ngàng ,hãnh diện,xấu hổ

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Mn ơi giúp mik với ạ mik đang cần gấp

Hợp chất là những chất được tạo nên từ bao nhiêu nguyên tố hóa học? A. Chỉ có 1 nguyên tố B.Chỉ từ 2 nguyên tố C.Chỉ từ 3 nguyên tố D.Từ 2 nguyên tố trở lên

Làm giúp mik câu 9 trở xuống với ạ

Ai làm giúp mình bài 2 với .....

Exercise 4: Rewrite these sentences: 1. Hurry up or we will be late for the last bus.  If 2. It was very cold yesterday, so we couldn’t go swimming.  If 3. He had a flu because he went out in the rain last night.  If 4. Ellen didn’t have much money in the bank, so she was very worried.  If 5. Stop talking or you won’t understand the lesson.  Unless 6. She can’t buy the dictionary because she doesn’t have enough money.  If Exercise 5: Choose the best answer: 1. If Jake ------------- to go on the trip, would you have gone? A. doesn’t agree B. didn’t agree C. hadn’t agreed D. wouldn’t agree 2. If energy ------------- inexpensive and unlimited, many things in the world would be different. A. is B. will be C. would be D. were 3. Unless you ------------- all of my questions, I can’t do anything to help you. A. answered B. answer C. would answer D. are answering 4. Had you told me that this was going to happen, I ------------- it. A. hadn’t believed B. don’t believe C. can’t believe D. would never have believed 5. -------------- interested in that subject, I would try to learn more about it. A. If I am B. Should I C. I was D. Were I 6. If I had enough money, --------------. A. I will buy that house B. I am buy that house C. I can buy that house D. I could buy that house 7. Had I had time, I -------------- to the beach with you this weekend. A. will come B. would come C. will have come D. would have come 8. If he -------------- that she was in the hospital, he -------------- to see her. A. knows/ will come B. knew/ would come C. had known/ would have come D. has known/will have come 9. If everything is all right, we -------------- our work on time. A. complete B. are completing C. have completed D. will complete 10. If I were you, I would work hard. A. You would rather not work so hard B. You should work harder C. You should work with me. D. Do not work so hard. 11. We didn’t visit the museum because we had no time. A. If we have time, we will visit the museum. C. If we had had time, we would have visited the museum. B. If we had time, we would visit the museum. D. If we had had time, we will have visited the museum. 12. -------------- I have time, I will go with you. A. If B. Unless C. So D. So that 13. -------------- harder, you would have passed the exam. A. If you studied B. If had you studied C. Had you studied D. Were you studied 14. If the police hadn’t saved me, I -------------- at that time. A. will die B. would die C. will have died D. would have died 15. -------------- at 4 o’clock, we would have missed seeing Bob. A. If we had gone B. Had we gone C. because we had gone D. A and B

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Câu 7. Tại sao ở các xe chở xăng dầu thường có một đoạn dây xích thả xuống mặt đường? Câu 8. Dùng một thanh thủy tinh đã được nhiễm điện đưa đến gần quả cầu kim loại treo trên giá. Ta thấy ban đầu quả cầu bị hút về thanh thủy tinh, sau khi quả cầu chạm vào thanh thủy tinh thì nó lại bị đẩy ra. Em hãy giải thích tại sao? Câu 9. Trong 1mm 3 vật dẫn điện có 30 tỉ electron tự do. Hãy tìm số electron tự do trong: a) 0,1m 3 vật dẫn điện b) Một sợi dây hình trụ làm bằng vật liệu ấy, có đường kính 0.2mm và chiều dài 10m Câu 10. Các electron đi qua một dây dẫn dài 12cm trong 10 phút. Hãy tính vận tốc của electron ra mm/s