Two resonance structures can be drawn for the formate ion, HCO2−. In structure A, the C–O bond to the hydroxyl oxygen (bond X) is a single bond, and in structure B, bond X is a double bond. Quantum calculations indicate that structure A contributes 70 % to the resonance hybrid, whereas structure B contributes 30 %. What is the bond order of bond X?
a) 1.5
b) 1.0
c) 1.3
d) 1.7