(a)Account for the following :
(i)The acidic strength decreases in the order `HCl gt H_(2)S gt PH_(3)`
(ii)Tendency to form pentahalides decreases down the group in group 15 of the periodic table.
(b)Complete the following chemical equations. :
(i)`P_(4)+SO_(2)Cl_(2)to`
(ii)`XeF_(2)+H_(2)O to`
(iii)`I_(2)+underset(("conc"))(HNO_(3)) to`

Explanation

(a) (i) This is due to the gerater polarity in HCL than `H_2S and H_2S` has more polarity then `PH_3` as Cl is more electronegate than S which is more electronegative than P. Hence bond dissociation energy of HCl is least and hence HCl is most acidic in nature.
(ii) Tendency to form pentohalides decreases down the group in group 15 due to inert pair effect, the outermost s-subshell electrons do not take part in bonding. Hence +5 oxidation state stability decreases down the group.
(b) (i) `P_4+10SO_4Cl_2to underset("Pentachloride")underset("Phosphorus")(4PCl_5)+10SO_2`
(ii) `XeFe_2+H_2Oto2Xe+4HF+O_2`
(iii) `I_2+underset(("conc."))(10HNO_3)tounderset("iodic acid")(2HIO_3+10N_2)+4H_2O`