Duduli

Noble gases being monoatomic have no interatomic forces except weak London dispersion force(which exist between two Noble atom e.g xe--xe when these are present near to each other), therefore they convert to Vapour at very low temperature. Hence they have low boiling points.

In group-16 down the group acidic character increases because down the group bond length between Hydrogen & group-16 element increase(due to large size of atoms)so bond strength decreases.Therefore H+ ion easily move from H2Te as compared to H2S,hence H2Te is more acidic than H2S.[A acid is said to be strong acid if it easily give H+ ion]

Answer:- NO2 contains odd number of valence electrons (5+6×2=17) it behaves as a typical odd molecule.On dimerisation it is converted to N2O4 which have even no. of electrons(5×2+6×4=34) which is stable. I.e