(a) Account for the following :
(i) The acidic strength decreases in the order `HCl gt H_2S 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_2Cl_2to`
(ii) `XeF_2+H_2Oto`
(iii) `{:(I_2+HNO_3to),(""" (cone)"):}`

Answer

(a)(i)HCl is stronger acid than HF.The acid strength of hydrogen halide is `HFltHClltHBrltHI`.
(ii)Element of this group form both ionic and covalent compounds in +3 oxidation state.In net shell, the covalent character decreases in the order :
`NgtPgtAsgtSbgtBi`.
Due to inert pair effect.
(b)(i)`P_(4)+10 SO_(2)Cl_(2)tounderset("Phosphorus pentachloride")(4PCl_(5)+10 SO_(2))`
(ii)`2XeF_(2)+H_(2)Oto2Xe+4HF+O_(2)`
(iii)underset(("conc."))(`I_(2)+10HNO_(3))tounderset("Iodine to Iodine acid")(2HIO_(3)+10NO_(2)+)4H_(2)O`