(a) Complete the following equations :
`PCl_(5)overset("heat")rarr`
(ii) `C+"Conc."H_(2)SO_(4)rarr`
(b) Explain giving reason in each case :
(i) Halogens are strong oxidising agents.
(ii) Fluorine form only one oxoacid, HOF.
(iii) Helium is used in diving apparatus.

Explanation

(i) `PCl_(5)overset(Delta)rarrPCl_(3)+Cl_(2)`
(ii) `underset("(Conc.)")(C+2H_(2)SO_(4))rarr2SO_(2)+CO_(2)+2H_(2)O`
(b) (i) Due to low bond dissociation enthalpy, high electronegativity and large electron gain enthalpy, halogens have strong tendency to accept electron. As a result, halogens act as strong oxidising agents.
`X_(2)+2r^(-)rarr2X^(-)`
(ii) Due to high electronegativity, small size, F cannot act as central atom in higher oxoacids in which the oxidation state F would be `+3,+5 and +7`. Hence, if formes an oxoacids i.e., HOF in which the oxidation state of F is `+1`.
(iii) Because of its low solubility (as compared to `N_(2)`) in blood, a mixture of oxygen and helium is used in diving apparatus used by deep sea divers.