[不定项选择题]共用题干 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 helium（氦）.Formerly,balloons con-
tamned 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 believed that noble gases couldn't chemically react at all.For this reason,they were
called inert gases(隋性气体）.They were also listed under Group 0 in the old periodic table because scien-
tists 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 right most
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 com-
plete,the atom is more reactive.Noble gases have a full outer shell,meaning that they have complete elec-
trons 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. MRI may make operating on the patient_________.
A.reactive
B.lightest
C.important
D.complete
E.flammable
F.unnecessary

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[不定项选择题]共用题干 Learn About Light

1 Ancient civilizations were amazed by the existence of light for thousands of years?The Greek philoso-
phrrs believed that light was made up of countless,tiny particles that enter the human eye and create what
we call vision.However,Empedocles and a Dutch scientist named Christian Huygens believed that light wag
like a wave.According to them,light spread out and travelled like a straight line.This theory was accepted
during the 19th century.
2 In 1905,Albert Einstein published a research paper in which he explained what is referred to as the
photoelectric effect.This theory explains that particles make up light.The particles Einstein was referring to
are weightless bundles（束）of electromagnetic（电磁）energy called photons（光子）.Today,scientists agree
that light has a dual（二重）nature一it is part particle and part wave. It is a form of energy that allows us to
see things around us.
3 Things that give off light are known as sources of light.During the day,the primary source of light is
the sun.Other sources of light include stars,flames,flashllights,street lamps and glowing gases in glass
tube.
4 When we draw the way light travels we always use straight lines.This is because normally light rays
travel in a straight line.However,there are some instances that can change the path and even the nature of
light. They are reflection,absorption,interference（干扰）,etc.
5 Physicists have attempted to measure the speed of light since the early times.In 1849,Hippolyte
Fizeau conducted an experiment by directing a beam of light to a mirror located kilometers away and placed
a rotating cogwheel（旋转齿轮）between the beam and the mirror. From the rate of rotation of the wheel,
number of wheel'S teeth and distance of the mirror,he was able to calculate that the speed of light is 313
million meters per second.In a vacuum（真空）,however,the speed of light is 299,792,458 meters per
second.This is about a million times faster than the speed of an airplane. Stars,flames,flashlights are some examples of_______.
A.sources of light
B.the speed of light
C.the path of light
D.a straight line
E.a beam of light
F.a form of energy

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