Correct Answer - (a)(i)Due to small size of fluorine atom, there are strong interelectronic repulsions in the relatively small 2p-orbitals of fluorine and thus, the incoming electron does not experience much attraction.
(ii)unlike `NH_(3),PH_(3)` molecules are not associated through hydrogen bonding in liquid state. That is why the boiling point of `PH_(3)` is lower than `NH_(3)`.
(a)(i)A mixture of helium and oxgen does not cause pain due to very low solubility of helium in blood as compared to nitrogen.
(ii)The fluorine atom has no d-orbitals in its valence shell and therefore cannot expand its octet.Being the most electronegative, it exhibits only-1 oxidation state.
(iii)The single O-O bond is weaker than the single S-S bond because of high interelectronic repulsion of the non-bonding electrons, owing to the small bond length.As a result the catenation tendency is weaker in oxygen.