How many valance are transferred from the nitrogen atom to potassium in the formation of the compound potassium nitride?

3 valence electrons are transferred in the formation of the compound potassium nitride because nitrogen needs 3 valence electron to become stable, or to have the electron configuration of noble Gases. 

Nitrogen requires 3 electrons to have a total of 8 valence electrons.Each potassium atom will transfer one electron.A total of 3 potassium atoms and one nitrogen atom will be involved  in the  formation of a formula unit of potassium nitride.

Anions are negative charged ions