Ta có công thức tổng quát của A là: XO₂

=> M_A=2.\(M_{O_2}\) = 2.32 = 64 (g/mol)

<=> M_X + 2M_O = 64

<=> M_X +32 = 64

=>M_X = 32 => X là: Lưu huỳnh (S)

=> Công thức hóa học của A là SO₂

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\(\dfrac{x+4}{2000}+\dfrac{x+3}{2001}=\dfrac{x+2}{2002}+\dfrac{x+1}{2003}\)

\(\dfrac{x+4}{2000}+1+\dfrac{x+3}{2001}+1=\dfrac{x+2}{2002}+1+\dfrac{x+1}{2003}+1\)

\(\dfrac{x+2004}{2000}+\dfrac{x+2004}{2001}=\dfrac{x+2004}{2002}+\dfrac{x+2004}{2003}\)

\(\dfrac{x+2004}{2000}+\dfrac{x+2004}{2001}-\dfrac{x+2004}{2002}-\dfrac{x+2004}{2003}=0\)

\(\left(x+2004\right)\left(\dfrac{1}{2000}+\dfrac{1}{2001}-\dfrac{1}{2002}-\dfrac{1}{2003}\right)=0\)

=> x+2004=0 => x=-2004

Tại mặt nước có hai nguồn sóng kết hợp S 1 ,   S 2 cách nhau 12 cm, dao động đồng pha nhau với tần số 20 Hz. Điểm M cách S 1 ,   S 2 lần lượt 4,2 cm và 9 cm. Biết tốc độ truyền sóng trên mặt nước là 32 cm/s. Để M thuộc vân cực tiểu thì phải dịch chuyển S 2 theo phương S 1 S 2 ra xa S 1 một khoảng tối thiểu bằng

A. 0,54 cm

B. 0,83 cm

C. 4,80 cm

D. 1,62 cm

Read the following passage and mark the letter A, B, C or D on your answer to indicate the correct word or phrase that best fits each of the numbered blanks.

Keeping your distance

Personal space is a term that refers (24) __________ the distance we like to keep between ourselves and other people. When (25) __________ we do not know well gets too close we usually begin to feel uncomfortable. If a business colleague comes closer than 1.2 meters, the most common response is to move (26) _________. Some interesting (27) __________have been done in libraries. If strangers come too close, many people get up and leave the building; others use different methods such as turning their back on the intruder. Living in cities has made people develop new skills for dealing with situations where they are very close to strangers. Most people on crowded trains try not to look at strangers; they avoid skin contact, and apologize if hands touch by mistake. People use newspapers (28) __________a barrier between themselves and other people, and if they do not have one, they stare into the distance, making sure they are not looking into anyone’s eyes.

Điền ô số 24

A. from

B. about

C. to

D. for

Mark the letter A, B, C, or D on your answer sheet to indicate the underlined part that needs correction in each of the following questions.

As far as I’m concerned, it was the year 2007 that Vietnam joined the World Trade Organization

A. concerned

B. the year 2007

C. that

D. the

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