Question

Which of the following is true about the bond length between atoms involved in resonance structures?

a. is exactly the same for all the same bonds in a population of molecules. 

b. changes in length every nanosecond or so, as the molecule switches from one resonance structure to another.

c. has one preferred position so that in each molecule, one of the bonds is shorter than the other.

d. has one preferred position so that one bond is shorter than the other, however, which bond is shorter may be different for each molecule, so the average of all resonance bonds in a mole of molecules is the same.