(a)Give reasons for the following : Nitric oxide becomes brown when released in air.
(b)Ammonia acts as a ligand. Why ?
( c)Assign a reason for the following: `SCl_(6)` is not known but `SF_(6)` is known.

Explanation

(a)Nitric oxide has one unpaired electron and hence is very reactive. As a result, it readily combines with `O_(2)` of the air to form nitrogen dioxide `(NO_(2))` which has brown colour.
`underset("Colourless")(2NO)+O_(2)tounderset("Brown")(2NO_(2))`
(b)Due to the presence of a lone pair of electrons 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")(AgCl)+ 2NH_(3) to underset("Diamminesilver(I)chloride")([Ag(NH_(3))_(2)]Cl)`
`underset("copper sulphate")(CuSO_(4))+ 4NH_(3) to underset("Tetraamminecopper(II)suplhate")([Cu(NH_(3))_(4)]SO_(4))`
`underset("Cromium chloride")(CrCl_(3))+ 6NH_(3) to underset("Hexaammine chromium(III)chloride")([Cr(NH_(3))_(6)]Cl_(3))`
(c )Fluorine is a much stronger oxidizing agent than chlorine, therefore, it can easily oxidise sulphur to its maximum oxidation state of `+6` and hence forms `SF_(6)`.Chlorine, on the other hand, being a weaker oxidizing agent can oxidies sulphur at the maximum to its `+4` oxidation state and hence can form `SCl_(4)` but not `SCl_(6)`.