The most stable Lewis structure of N2O is:

the stable Lewis structure has following property

a complete octet of every atom and formal negative charge must be on more electronegative  atom and formal positive charge must be on the electropositive atom.                 

The charge separation should be minimum. 

In structure number (D) the octet of atoms are complete and formal positive positive charge is on less electronegative Nitrogen and formal negative charge is on more electronegative Oxygen atom.

The correct option is (D)