Give reasons for the following :
(i) Nitric oxide becomes brown when released in air.
(ii) Solid phosphorus pentachloride exhibits some ionic character.
Or `PCI_(5)` is ionic in nature in the solid state.
(iii ) Ammonia is a good complexing agent.
Or Ammonia acts as a ligand

Explanation

(i) Nitric oxide readily combines with `O_(2)` of the air to form nitrogen dioxide `(NO_(2))` which has brown colour.
`underset("(Colourless)")(2NO+O_(2))rarr underset("(Brown)")(2NO_(2))`
(ii) `PCl_(5)` is ionic in the solid state because it exists as `[PCl_(4)]^(+)[PCl_(6)]^(-)` in which the cation is terahedral and the anion in octahedral.
(iii) Due to presence of a lone pair of electron on `N, NH_(3)` acts as a complexing agent (ligand). As a result, it combines with transition metal cations to form complexes.
For example :
`underset("Silver chloride Diamminesilver (I) chloride")(AgCl+2NH_(3)rarr[Ag(NH_(3))_(2)]Cl)`
`underset("Copper sulphate Teraamminecopper (T) sulphate")(CuSO_(4)+4NH_(3)rarr[Cu(NH_(3))_(4)]SO_(4))`
`CrCl_(3)+6NH_(3)rarr underset("chloride")underset("Hexaamminechromium (III)")([Cr(NH_(3))_(6)]Cl_(3))`