Give reason to explain +5 oxidation state is less stable than the +3 state in Bismuth.

Explanation

Because the nitrogen atom in ammonia has a lone pair of electrons which it can easily lose and act as a ligand, Due to small size of nitrogen atom, the lone pair of electrons is distributed over a smaller area. This increases the availability of electron pair and hence the basic character of `NH_3`. Due to greater availability of lone pair of electrons, `NH_3` is a good complexing agent also.