# NEET Chemistry The p-Block Elements (XII) Questions Solved

BOARD

(a) 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.

(b) Draw the structures of the following molecules :

(i) $Xe{F}_{2}$                                                (ii) ${H}_{2}{S}_{2}{O}_{8}$

(a) (i) Helium is used in diving apparatus because of its very low solubility in blood and therefore an oxygen-helium mixture is used for artifical respiration.

(ii) Because it is most electronegative element and does not have d-orbitals for octet expansion, therefore it shows only a negative oxidation state of -1.

(iii) The greater catenation tendency of sulphur is due to two reasons :

(a) The lone pair of electrons feels more repulsion in O-O bond than S-S bond due to its small size and thus S-S forms strong bond.

(b) As the size of atom increases down the group from O-PO, the strength of bond increases and therefore catenation tendency also increases.

(b) (i) $Xe{F}_{2}$ :

Shape : Linear

Angle : $F-Xe-F>90°$

(ii) ${H}_{2}{S}_{2}{O}_{8}$ :

Difficulty Level: