Which of the following is considered to be the fifth state of matter?

Bose-Einstein condensate

The correct answer is option 1. Bose-Einstein condensate.

The fifth state of matter, known as Bose-Einstein condensate (BEC), is a unique and fascinating form of matter that occurs at extremely low temperatures close to absolute zero (approximately -273.15 degrees Celsius or 0 Kelvin). This state of matter was first predicted by Albert Einstein and Indian physicist Satyendra Nath Bose in the 1920s based on the principles of quantum mechanics.

In a Bose-Einstein condensate, a group of bosons (particles with integer spin, such as photons, helium-4 atoms, and certain types of atoms like rubidium and sodium) are cooled to temperatures near absolute zero, causing them to occupy the same quantum state. At these ultracold temperatures, the individual wavefunctions of the particles overlap, and they lose their distinct identities, behaving collectively as a single quantum entity.