The best diagram to represent N2O is the second diagram.
The Lewis diagram is used to represent the way two or more atoms bond. This is possible by using lines to represent bonds and dots to represent electrons.
In the case of the molecule N2O bonding occurs in the following way:
A triple bond is formed between the nitrogen atoms, which means, in the Lewis diagram the nitrogen atoms are connected with three lines.
The oxygen atom connects to one of the nitrogen atoms.
The nitrogen atom that is not connected to the oxygen will have 2 electrons represented by dots because the number of valence electrons is 5, but three were used in the triple bond.
The oxygen atom will have 6 electrons represented by dots, which are equal to the number of valence electrons.
