The correct answer is option 2 - Bose-Einstein condensate.

Solid, liquid, gas, and plasma are the four states of matter that are commonly known. However, in 1995, a new state of matter called Bose-Einstein condensate (BEC) was discovered by physicists Eric Cornell, Carl Wieman, and Wolfgang Ketterle.

Bose-Einstein condensate is a unique state of matter that occurs at extremely low temperatures, close to absolute zero (-273.15 degrees Celsius or -459.67 degrees Fahrenheit). In this state, a group of atoms or particles, known as bosons, come together and lose their individual identities, behaving as a single entity with wave-like properties.

Bose-Einstein condensate exhibits fascinating phenomena, such as superfluidity and quantum coherence, which are not observed in other states of matter. It has provided valuable insights into quantum mechanics and has opened up new avenues of research in fields like atomic physics and condensed matter physics.

In summary, Bose-Einstein condensate is a unique state of matter that was discovered in 1995 and exists at extremely low temperatures, demonstrating remarkable quantum properties.