Question

Which of the following species is not expected to be a ligand?
(a) NO
(b) $N{H}_4^{+}$
(c) $N{H}_{2}C{H}_{2}C{H}_{2}N{H}_2$
(d) CO

Answer 1

Ligand must donate a pair of electron or loosely held electron pair to metal and form M - L bond.
e.g.,
$:\stackrel{..}{N}=O,\stackrel{..}{N}{H}_{2}C{H}_{2}C{H}_2\stackrel{..}{N}{H}_2,:CO$
Among $\stackrel{+}{N}{H}_4$ does not have any pair of electron.
Hence, the answer (b) $\stackrel{+}{N}{H}_4$ is not a ligand.