Explanation:

Formal Charge:-

Formal charge (FC) is the charge ASSIGNED to an atom in a molecule, assuming that electrons in all chemical bonds are SHARED equally between atoms, regardless of relative electronegativity.[1] When determining the best Lewis structure (or predominant resonance structure) for a molecule, the structure is chosen such that the formal charge on each of the atoms is as close to zero as possible.

credits: Wikipedia

Formula for formal charge:-

FC= V-N- (B/2)

where,

V is the number of valence electrons of the neutral atom in isolation (in its ground state);

N is the number of non-bonding valence electrons on this atom in the molecule;

B is the total number of electrons shared in bonds with other atoms in the molecule.

1) Here,

Hydrogen has 1 valence electron always and it has no election left to be shared and it is sharing 2 electrons with C ( single bond) so the values to be put in formula for hydrogen become 1-0-(2/2) =0

Similarly for C

the valence electrons for carbon are always 4

in the given formula we can see that there is no electron left for sharing and it is sharing 8 electrons 6 with N ( 3 bonds) and 1 with H ( single bond) hence the values in the formula become 4-0-(6/2)=0

Same goes for N

5 valence electrons

1 lone pair so 2 electrons

6 shared electrons (3 bonds with C)

so, 5-2-(6/2)=0

2) Now here the position for N and C are interchanged, which makes it interesting.

The CASE with H will remain the same as it is still having single bond and it is able to achieve its stable state without any problem, no matter where it gets its electron from.

But for N, whose TENDENCY is to gain electrons, is now having 4 binds, one with H and 3 with C

so, it has exhausted it's lone pair of electrons.

The valence electrons of N is 5 the free electrons of N now is 0 and the shared electrons of N is 8 ( 4 bonds)

so the formal charge is 5-0-(8/2)=+1

Now for C, here as usual its valence electrons will be 4, but now it will have one lone pair of electrons as it has formed on 3 bonds as opposed to the usual bonding of 4. Also, because it has formed three binds, therefore, its shared electrons will be six.

hence, its formal charge will be 4-2-(6/2)=-1

Now, what is important to note here is that N usually does not have +ve charge but here it has it and same goes for C, it does not have negative charge but here it has it.

So, keep in mind that Formal Charge is NOT REAL CHARGE, IT IS FAKE CHARGE.

3. In this Ozone formula also, you will see that one of the oxygen atoms will have +1 other will have -1 and third will have 0 formal charge.

The formal charge appears to keep the molecule stable.

Hope this helps!

P.S. Warning scared me! :p