Bài tập 15: Một công thức oxit của lưu huỳnh chứa 50% Oxi , 1g khí chiếm 0,35 lít ( ĐKTC) . Xác định công thức hóa học của oxit trên ? ( S =32, 0 =16 )

Bài tập 14: Nguyên tố X có thể tạo thành với Al hợp chất AlaXb , mỗi phân tử gồm 5 nguyên tử , PTK là 150 . Hãy xác định nguyên tố X?

Bài tập 13: Hai nguyên tố A và B đứng kế tiếp nhau trong chu kì thuộc bảng hệ thống tuần hoàn , có tổng số điện tích hạt nhân là 20. Hãy xác định 2 nguyên tố A và B ?

Bài tập 12: Dùng bảng tuần hoàn các nguyên tố hoá học hãy : a, Viết công thức oxit cao nhất và hợp chất với hidro của các nguyên tố trong chu kì 3 b, Nguyên tố nào trong chu kì 3 có tính kim loại mạnh nhất ? Tính phi kim mạnh nhất ?.

Đề bài:complete the passage with a suitable preposition. We have English lessons(1)______Room 12.There are 24 tables for students and one desk for the teacher.(2)_____the walls,there is a lots of posters of England.There's a cupboard at the front of the room and(3)_____the cupboard,there is a TV and DVD player.Sometimes we watch films.There are some bookshelves(4)_____the classroom.(5)_____the shelves,there are a lot of English books.Our books are(6)_____the teacher's desk.He wants to look at our homework.Our school bags are(7)_____the floor,and there is some food(8)_____the school bags.It's now 5.30 pm.We are(9)_____home,but our teacher is(10)_____school.He often stays late to prepare for tomorrow's lessons.

một người dùng mặt phẳng nghiêng để đưa một kiện hàng nặng 100 kg từ dưới đất lên sàn xe tải. Người đó dùng một lực kéo tối thiểu là : a. F<1000N b.F=1000N c.F>1000N d.F=2000N

VIII. Complete the following sentences with the correct form of the words in brackets. 1. Street are decorated with ________________ lights and red banners. (colour) 2. There are many _________ differences between the two communities. (culture) 3. She gave a wonderful ________________ as the Iron Lady – the former British Prime Minister Margaret Thatcher. (perform) 4. There were lively New Year ________________ all over the town. (celebrate) 5. When we heard she’d got the job, we all went off for a ________________ drink. (celebrate) 6. It is ________________ in America to eat turkey on Thanksgiving Day. (tradition) 7. What forms of ________________ do you participate in during the festival? (entertain) 8. The hall looked very ________________ with its Christmas tree. (festival) 9. Her eyes were wide with ________________ when she heard the news. (excite) 10. The Chinese New Year marks the ________________ of spring and the start of the Lunar New Year. (begin) XI. Read the text and choose the best answers: SAFETY TIPS FOR BUS PASSENGERS Always maintain a queue while waiting (1)______ a bus. Never stand on queue on the middle of the road. At the time of boarding a bus do not try to run or chase the bus. Once you are inside the bus, (2)______ a seat and hold firmly on the handrail if you are standing. Never try to (3)______ an overcrowded bus. Avoid (4)______ inside of a bus because your high-pitch noise may distract the attention of the driver and it could lead to a major (5)______ accident. 1.A.for B.to C.on D.in 2.A.hold B.sit C.take D.find 3.A.choose B.go C.wait D.board 4.A.shout B.shouting C.to shout D.shouts 5.A.road B.way C.path D.street XVI. Rewrite the sentences in the passive voice. 1. We usually lock the safe carefully. The safe .......................................................................................................... 2. We keep the safe in the bedroom on the second floor. The safe .......................................................................................................... 3. Yesterday the thieves stole everything in it. Yesterday everything in it .............................................................................. 4. We told the police about it. The police ....................................................................................................... 5. The police checked everything in the house. Everything in the house .................................................................................. 6. The police questioned everybody in the house. Everybody in the house .................................................................................. 7. The police surrounded the house. The house ....................................................................................................... 8. The police did not think that they caught the thieves. The police did not think that the thieves ......................................................... 9. We will use less electricity in the future. Less electricity ……………………….. 10.The students in my school will use public transport when travelling long distances. Public transport …………………… 11.I will turn off the lights when leaving a room or going to bed. The lights …………………….. 12.Wind power will offer a great deal of energy next century. A great deal of energy ……………… 13.We will use sources of energy more effectively for our future. Sources of energy ……………………. 14.People in the countryside will increase the use of biogas for cooking. The use of biogas …………………. 15.They will build a hydro power station in the North of the country next decade. A hydro power station ……………. 16.We will solve the problem of energy shortage by using solar energy. The problem of energy shortage …………..

Để ghi nhớ công lao của Hai Bà Trưng hằng năm ta kỉ niệm vào thời gian nào?

Hòa tan hoàn toàn hh X gồm Fe và Mg bằng lượng đủ HCl 20% thu dd Y. Biết C% MgCl2 trong dd Y là 11.787%. Tính C% muối sắt trong dd Y.

các bn giải giùm mình nha. ro ko có TV nên mình chọn bừa các bạn thông cảm giùm mình nha.