Question

Which of the following is a superfluid?
(A) Krypton
(B) Argon (II)
(C) Helium (II)
(D) Helium (I)

Answer 1

Liquid when it flows through a surface encounters some resistance. The resistance it encounters is called viscosity. When this resistance is absent then we call this as a superfluid. Real gases liquify at a certain temperature and this temperature is called critical temperature. The process is said to be liquification of gases.

Step by step explanation:
Any substance that occupies space and has mass is called matter. The matter usually exists in 3 states that can be solid, liquid and gas. The solid state is a state where the interparticle distance is the least and hence the matter has a definite shape and size. Liquid does have inter particle space and has the ability to flow. During the flow of liquid on the surface, it is assumed that it flows in layer as one layer flows some amount of restriction is encountered by the next layer. This resistance is called viscosity. Gases too have viscosity but it is very negligible. In case of superfluid there is no any resistance that it encounters while flowing hence it has 0 viscosity and thus can flow freely.
This property or state in a liquid is demonstrated by only a few isotopes of helium. The temperature is extremely low. The gas at a very low temperature can liquify as we know from the fact of liquefaction of gas. Thus, the isotope of helium is helium (II).

Note:
Isotope are substances which have the same atomic number and different mass number. Thus, the number of neutrons vary in these cases. There are more than 100 isotopes present in the periodic table. Examples: hydrogen, deuterium and tritium.