Statement-I : In the case of Nitrogen all the oxidation states from  + 1 to + 4 tends to  undergo disproportionation  in acidic solution

Statement-II : In the case of  phosphorous nearly all  the oxidation states readily undergoes disproportionation in acidic and alkali medium

Statement I is true 

Nitrogen compounds in + 1 to + 4 oxidation states, nitrogen contains lone pair electrons and under goes disproportionation in presence of acidic medium. These oxidation states are intermediate oxidation states.

Statement II is false 

P shows oxidation states from - 3 to +5. Only those oxidation states in between - 3 to +5 under goes disproportionation in both acidic and basic medium but not all oxidation states .