wt gas has lowest boiling pt??

Helium has the lowest boiling point of any substance.

Noble gases have low boiling and melting points because they have very weak interatomic attractions or forces. The motions of the atoms of the noble gases must be slowed down before the weak London dispersion forces can lock the atoms into place to form a solid.

KakaYee 's answer is correct. He has the lowest boiling point.

Melting point(at 2.5 MPa) 0.95 K, −272.20 °C, −457.96 °F
Boiling point4.222 K, −268.928 °C, −452.070 °F

from wiki