In the cyanate ion, OCN-, carbon is the central atom. (b) Which resonance structure makes the greatest contribution to the resonance hybrid? Which makes the least contribution? Explain.

Resonance structures are different Lewis structures for a molecule that can be drawn by moving electrons around while keeping the positions of the atoms fixed. These structures represent the same molecule but differ in the distribution of electrons, particularly in the placement of double bonds and lone pairs. The actual structure of the molecule is a resonance hybrid, which is a weighted average of all valid resonance forms.

Formal charge is a theoretical charge assigned to an atom in a molecule, calculated based on the number of valence electrons, the number of non-bonding electrons, and half the number of bonding electrons. It helps in determining the most stable resonance structure, as the structure with the lowest formal charges on atoms is generally more favorable. A formal charge of zero on all atoms is ideal, but if not possible, the negative charges should reside on the more electronegative atoms.

Electronegativity is a measure of an atom's ability to attract and hold onto electrons in a chemical bond. In resonance structures, the placement of charges is influenced by electronegativity; more electronegative atoms are better suited to bear negative charges. Understanding electronegativity helps in evaluating which resonance structures are more stable and thus contribute more significantly to the resonance hybrid.