The Lewis formula is structural representation that indicates the bonding between atom of a molecule by line and dots used to indicates the electron position around the atoms, electron pair is known as lone pair of electrons shown by pair of dots. The electrons indicated in the structure are valence electrons.

The given atoms are N (g) and O (g).

N (g), whose atomic number is 7.

Electronic configuration for N (g) is 2, 5.

Number of valence shell electrons for N (g) is 5.

O (g), whose atomic number is 8.

Electronic configuration for O (g) is 2, 6.

Number of valence shell electrons for O (g) is 6.

The Lewis formula for N (g)  and O (g) is shown in the image.

The atoms combine to form molecule in order to complete their octet that is to get 8 electrons in their valence shell and get stabilize in nature.

The total number of valence shell electrons in NNO(g) is:

2(5)+6 = 16 electrons

The distribution of electrons in the atom will take place in such a way that formation of triple bond will take place between two nitrogen atoms and a single bond will form between nitrogen and oxygen atom. In order to complete their octet, the nitrogen atom in center will possess 1+ formal charge and oxygen will possess 1- charge (oxygen is  electronegative atom). Thus, results in formation of neutral molecule.

The formal charge on each atom is calculated using:

Valence electrons - Nonbonding electrons - frac{Bonding electrons}{2}

The Lewis formula of NNO(g) is shown in the image.