The number of isomers possible for
[Pt(en)(NO₂)₂] is :

The pair in which both the species have the same magnetic moment (spin only) is :

The intermolecular potential energy for the molecules A, B, C and D given below suggests that :

On heating, lead (II) nitrate gives a brown gas (A). The gas (A) on cooling changes to a colourless solid/liquid (B). (B) on heating with NO changes to a blue solid (C). The oxidation number of nitrogen in solid (C) is :