Account for the following:

(i) Helium is used in diving apparatus.

(ii) Fluorine does not exhibit positive oxidation state.

(iii) Oxygen shows catenation behaviour less than sulphur

(i) Helium mixed with oxygen under pressure is given to sea-divers for respiration. However, pure oxygen can be toxic at great concentrations at the depth. Therefore oxygen can be mixed with helium to reduce oxygen concentration while eliminating nitrogen. During controlled decompression, the helium would also diffuse out of tissue and the lungs are more easily than nitrogen avoiding the bends .Use of helium for relatively shallow scuba diving would likely permit longer driving times with less threat of the bends.

(ii) Fluorine being the most electronegative atom does not exhibit positive oxidation state because the electrons in fluorine are strongly attracted by the nuclear charge because of the small size of a fluorine atom and therefore, removal of an electron is not possible.

(iii) Sulphur shows catenation behaviour more than that of oxygen because the oxygen atom is smaller in size as compared to sulphur, the O-O bonds in oxygen experiences repulsions due to the lone pairs present on oxygen atom and therefore, are weaker as compared to the S-S bonds.