Which of the followings is not a intramolecular redox reaction?

Explanation:

Disproportionation redox reaction- it is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states.
Intramolecular redox reaction- in this reaction one atom of a molecule is oxidized and another atom of the same molecule is reduced.

NH4NO2               →           N2                 +              2H2O
Oxidation state-            -3     +3                          0

                                                               NH4NO3                 →           N2O        +              2H2O
Oxidation state-            -3    +5                           +1
                                                                 
                                                             2KClO3                    →           2KCl       +              3O2

Oxidation state-            +5                                  -1                             0

Final Answer:
Hence, Option (D) is correct.

The following reaction shows disproportionation reaction 2H2O2 → 2H2O + O2.