Answer:
electronegativity
Step-by-step explanation:
When electrons are shared between two or more than two atoms in a compound, the tendency of one atom can be more than other atom to attract the shared electrons towards it self. This tendency is called electronegativity. For example, Hydrogen has electronegativity of 2.0 while for Oxygen it is 3.5. So in molecule of water, oxygen has better tendency to attract the shared electrons more towards itself than that of Hydrogen.
It is also called as mesomerism and it describes delocalized electrons of a polyatomic molecule or any other molecule where bonding cannot be demonstrated through only one structure.
Ionization is simply the process in which atom gains a charge when it gains or loses an electron. For example, When Sodium atom loses electron it form sodium ion (Na+).
It is a process during which atomic orbitals mix into hybrid orbitals in such a way that newly formed orbitals have different energies and shapes than original orbitals.
Therefore, we can clearly see that option D electronegativity is the best option.