Which of the following scenarios are inappropriate uses of noble gases? Which of the following applications is inaccurate?
  1. Helium and Argon are used to produce inert atmospheres for welding
  2. Helium is suitable to fly air balloons and airships
  3. Neon, Argon, Krypton and Xenon are used to impart different colours in “neon lights”
  4. Liquid Helium can be used to cool apparatus close to 1 K. This is particularly impressive to cool superconducting magnets that produce very high magnetic fields
  5. None of the above


The correct option is E None of the above
All these noble gases are nearly inert (except Xenon and to a small extent, Krypton). Definitely they can be used to create inert atmospheres – particularly Argon. Helium is much lighter than air and it is used to keep airships and air balloons afloat in the air. Owing to abundance, Argon is manufactured on a much larger scale than the other noble gases. It finds extensive application in high-temperature metallurgical processes as an inert atmosphere.
Helium is extremely difficult to solidify even at 1 K. At this temperature, a pressure of 2.5 MPa is needed to solidify the liquid Helium! This property is utilized to cool superconducting magnets which become superconducting at very low temperatures. Liquid Helium is a subject of tremendous interest in the scientific community. At 100 kPa, the gas liquefies at 4.2 K. Let us call this Helium-I. When this liquid is cooled further to about 2.2 K, the properties of the liquid change dramatically. Let us call this Helium-II. Its viscosity drops to 0!
Helium-II conducts heat 106 times better as compared to the thermal conductivity of Helium-I.
In what is popularly referred to as “neon signs”, using different gases like He, Ne, Ar, Kr & Xe inside the tubes produce characteristic colours depending on the gas used. For example, neon gives red light and helium yellow light. Xenon flash lamps produce short bursts of UV and visible
light. Further, these noble gases are also used in lasers (helium–neon, argon-ion, and krypton-ion lasers).
As we can see, all the uses are appropriate. Hence,
e) none of the above

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