Explain the following:
(a) `H_2S` is a gas while `H_2O` is liquid at room temperature.
(b) Ionization energies of noble gases are very high.
(c) Why is ammonia a good complexing agent ?
(d) Name a compound in which iodine shows positive oxidation state.

Explanation

(a)` H_2O` has higher boiling point than `H_2S` , because hydrogen is bonded to electronegative element oxygen and, therefore, it can form hydrogen bonds. As a result, water exists as associated molecules and, therefore, exists as a liquid
(b) The ionisation energies of noble gases are very high. This is due to stable completely filled electronic configurations of their atoms. Noble gases : `ns^2 np^6`
As a result, very large amount of energy is required to remove the electron.
(c) Ammonia is a good complexing agent because of the presence of lone pair of electrons on nitrogen. This lone pair can easily be donated to electron deficient species (transition metal ions) to form complexes.
(d) Iodine shows positive oxidation state in ICI. The evidence for positive oxidation state of iodine is that when ICl is electrolysed, iodine is liberated at cathode while both `I_2` and `Cl_2` , are liberated at anode. The liberation of iodine at cathode indicates the presence of cationic iodine.
`2ICl iff I^(+) + ICl_(2)^(-)`