Question

Which of the following statements regarding Helium is incorrect?
A) It is used to fill balloons instead of hydrogen because it is lighter and non-inflammable.
B) It is used as a cryogenic agent for carrying out experiments at low temperature.
C) It is used to produce and sustain powerful superconducting magnets.
D) It is used in gas-cooled nuclear reactors.

Answer 1

Helium is a noble gas whose atomic number is two and it belongs to the 18th group and the second of the period of the periodic table. It is used for varied application due to its inertness in properties.

Complete step by step solution:
Helium is a light gas, lighter in comparison to air which is mostly nitrogen and oxygen and it is non-inflammable in nature, and hence it is used to fill air-balloons. But helium is not lighter than hydrogen gas as its atomic weight is 4 while the molecular weight of hydrogen is 2. Hence statement A is incorrect.
Helium does not freeze at atmospheric pressure and only at pressures that are 20 times the atmospheric pressure will the helium freeze. Hence, liquid helium, because of its low boiling point, it is used in many cryogenic systems when temperature below the boiling point of nitrogen is needed.
Liquid helium is used as a coolant for many superconducting windings. It has a boiling point of 4.2$$$$\text{K}, far below the critical point of most winding materials.
Both helium and carbon dioxide are used to cool nuclear reactors.

Hence, the incorrect option is A.

Note:
Carbon dioxide is used in the gas-cooled nuclear reactors, absorbing the heat from the surrounding elements and reaching ${{650}^{0}}\text{C}$. Hydrogen gas is 7% more buoyant than helium but helium is preferred over hydrogen due to the fire risks associated with it. But when it comes to weight, helium is heavier in comparison to hydrogen.