A visual representation of covalent bonding which represents the valence shell electrons in the molecule is said to be a Lewis structure. The lines represents the shared electron pairs and dots represents the electrons that are not involved in the bonding i.e lone pairs.
Number of valence electrons in each atom:
For Carbon, 
= 4
For Hydrogen, 
= 1
For Nitrogen, 
= 5
The Lewis structure of 
is shown in the attached image.
The formula of calculating formula charge = 
-(1)
where, F.C is formal charge, V.E is number of valence electrons, N.E is number of non-bonding electrons and B.E is number of bonding electrons.
Now, calculating the formal charge:
For on left side:
For :
For on right side:
The formula charge of each atom other than hydrogen is shown in the attached image.
B) energy is absorbed by the reaction
is right answer.
The part of the atom that is involved in chemical changes is A. electron. The electrons that are in the most outer shells are called valence electrons which are easily removed or shared to form bonds. Valence electrons are related to the number of valence electrons
D should be the correct answer. isotopes are atoms that have the same atomic number (number of protons) but different atomic masses (number of protons and neutrons). isotopes also have the same number of electrons since atoms need to have equal numbers of protons and electrons to not be considered ions. Since the number of protons determines the chemical properties of the atom, we can say that all isotopes have the same chemical properties due to the fact that all isotopes have the same atomic number.
I hope this helps. Let me know in the comments if anything is unclear.
