Question

Helium is used: (Multiple correct options can be possible)
(A) As a refrigerant (in liquid form) in low temperature physics
(B) As a substituent for Nitrogen in the breathing gas for deep-sea divers
(C) In radiation therapy
(D) In fluorescent tubes

Answer 1

Helium is an inert gas, who is also a very light gas that makes it rapidly diffusing gas. Also at low temperature helium is a good conductor of heat and it is less expensive, easy to store gas and even at high pressure it has very low solubility in fluids like blood. All these properties make it find a wide range of applications.

Complete answer:
Helium is a good choice as a refrigerant because its properties allow components to be kept cool over long distances. At atmospheric pressure gaseous helium becomes liquid at around 4.2 K (-269.0°C). However, if cooled below 2.17 K (-271.0°C), it passes from the fluid to the superfluid state. Superfluid helium has remarkable properties, including very high thermal conductivity; it is an efficient heat conductor. These qualities make helium an excellent refrigerant for cooling and stabilising the LHC's large-scale superconducting systems.
Air, which was first used in diving tanks, contains roughly 20% oxygen, and 80% nitrogen. The trouble with nitrogen in this situation is that nitrogen is a fairly heavy gas, and is soluble in blood at high pressure. Long term use of nitrogen can cause extreme nerve pain and nausea. To avoid all these problems is to avoid the nitrogen. Divers who work at depth or for long periods use a mixture of 20% Oxygen and 80% Helium. Helium is used for a number of reasons – It is light, cheap, and does not dissolve in blood the same way that nitrogen does. Being inert it cannot be toxic to the diver or corrosive to equipment.
It has been demonstrated that the use of helium ions in radiation therapy could provide accurate treatment to tumors while helping to spare healthy organs.
A fluorescent lamp tube is filled with a mix of argon, xenon, neon.

So Option (A), (B) and (C) are the correct choice for this question.

Additional information: helium has mass number 4 that makes it very light gas along with atomic number 2 that gives it fulfilled electronic configuration that makes it inert.

Note: helium is a colorless, tasteless, odorless, non-toxic gas. It is the second highest and second lightest gas in the universe after hydrogen. It has the lowest boiling point among all the elements in the periodic table. It is abundant in the sun that justifies that a large amount of helium is created by nuclear fusion at the sun's surface which requires very high temperature.