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Learn about Noble Gases（惰性气体）

1 Have you ever ridden on a balloon?Many tourist spots offer balloon rides in order for people to see the beauty of a place from above. A balloon contains a noble gas called hellum（氦）. Formerly,balloons contained hydrogen but hydrogen is very flammable and dangerous when uncontrolled. Therefore,people shifted to helium,which is safer. Helium is safe because it has the properties of the noble gases.

2 People once belleved that noble gases couldn't chemically react at all. For this reason,they were called inert gases（惰性气体）. They were also listed under Group 0 in the old periodic table because scientists believed that the gases have zero valence（价）electrons in their outer shell. This was later proven to be untrue when some noble gas compounds were discovered.

3 The gases are elements,which share similar properties. These properties include being monoatomic,colorless,odorless,being able to conduct electricity,and having low chemical reactivity. Noble gases include Helium,Neon,Argon,Krypton,Xenon and Radon. These are all found in Group 18,in the rightmost column of the periodic table. If you look at the periodic table,you will notice that these elements are the only ones,which do not have a charge. Helium has the lowest molecular（分子的）weight while Radon is the heaviest.

4 Remember that chemical reactions occur because atoms have valence electrons,which are electrons in their outer shell. When the outer shell is "unfilled" or the required number of electrons is not yet complete,the atom is more reactive. Noble gases have a full outer shell,meaning that they have complete electrons in their outer shell. This complete number varies. For instance,the outer shell of Helium has 2 valence electrons while the outer shell of Xenon has 8 electrons. Nowadays,there remains to be a few noble gases because of the low chemical reactivity of these said gases.

5 because of their properties,noble gases have many important applications. They are widely used in medicine and industries. For instance,liquid Helium is used for superconducting magnets（磁体）. These magnets are very important in physics and medicine. When a doctor suspects that a person's brain has been damaged,he might request for Magnetic Resonance Imaging（MRI）. MRI allows the doctor to "see" the brain,without operating on the patient.

A. How were noble gases discovered?

B. what is the periodic table?

C. what are the applications of noble gases?

D. How were noble gases understood in the past?

E.What causes the low chemical reactivity of noble gases?

F. What are noble gases?

23. paragraph 2________

[参考答案]E

[解析]第二段主要讲述过去人们曾以为惰性气体是完全没有活性的.所以E选项How were noble gases understood in the past?"人们过去是如何理解惰性气体的"正确.

24. paragraph 3________

[参考答案]C

[解析]第三段主要解释什么是惰性气体,惰性气体具体包含哪些气体以及惰性气体元素在元素周期表的位置等.所以C选项What are noble gases?"什么是惰性气体"贴合段意.

25. paragraph 4________

[参考答案]D

[解析]第四段主要讲述惰性气体的化学性质稳定,是因为最外层电子满足稳定结构.所以 D选项What cause the low chemical reactivity of noble gases?"惰性气体化学性质不活跃的原因"正确.

26. paragraph 5________

[参考答案]A

[解析]第五段第一句Because of their properties,noble gases have many important applica— tions就讲明主旨：由于其特性惰性气体有很多重要应用.所以A选项What are the applications of no— ble gases?"惰性气体的应用"正确.

A. complete

B. reactive

C.unnecessary

D. flammable

E. important

F. lightes

27. Noble gases are not very chemically .

[参考答案]F

[解析]题意：惰性气体化学性质不…….根据第三段第二句These properties include being monatomic,colorless,odorless,being able to conduct electricity,and having low chemical reactivity可知惰性气体化学性质不活泼.故F选项"活跃的"合适.

28. Among the elements of noble gases Helium is the .

[参考答案]C

[解析]题意：在惰性气体中,氦是…….

根据文中的第三段最后一句Helium has the lowest molecular weight while Radon is the heaviest可得知,氦气是所有惰性气体中最轻的.故选C.

29. The required number of electrons in noble gases'outer shell is .

[参考答案]B

[解析]题意：惰性气体外层电子数应为…….根据第四段第三句Noble gases have a full outer shell,meaning that they have complete electrons in their outer shell可得知,惰性气体外层电子数应全满.故选B.

30. MRI may make operating on the patient .

[参考答案]A

[解析]题意：磁共振成像（MRI）可使手术…….根据第五段最后一句MRI allows the doc— tot t0"see"the brain,without operating on the patient可知,通过MRI,医生可以不通过手术就看到患者头部影像.故选A.