Question

Resistance of mercury at 4.2K is
A. infinity
B. greater than at lab temperature
C. same as that of lab temperature
D. Almost zero

Answer 1

Onnes on 8th April 1911 discovered that below 4.2K (about -269°C), the resistance of mercury suddenly became zero. The experiment later repeated several times showing a very sudden drop which amaze all of us which is inexplicable.

Complete step by step answer:
First of all let us check the history of resistance of mercury at 4.2 K
Onnes, on 8th April 1911 discovered that below 4.2 K resistance of mercury suddenly reduced to zero which was a great breakthrough into the field of superconductors.
Superconductors are different categories of materials with a resistivity tends to zero. It is having a lot practical applications in our day to day life. Superconductors are special materials in which no energy loss or current loss is happening. Because of this property they are used widely in MRI scanning and all. Even though superconductors should be cooled to temperatures only a few kelvin above absolute zero. This is a very costly procedure. it is a disadvantage of superconductors.in the past few decades so many further discoveries happened in this field. Now we have found that some materials change their nature into superconductivity at higher temperatures. World is waiting for more and more discoveries.
Onnes was awarded the Nobel Prize for this in 1913. He is the first person to liquefy the helium which is also a huge discovery in the world of physics.

Note:
This is a general knowledge kind of question. Try to learn it and remember it. At zero kelvin energy becomes zero reducing the movement of electrons. Onnes was awarded the Nobel Prize for this in 1913. He is the first person to liquefy the helium which is also a huge discovery in the world of physics.