Chemistry - GOC Question with Solution | TestHub

Both cations are tertiary. In (b) the $\mathrm{C}=\mathrm{C}$ is next to the cation, so it is allylic and has resonance. In (a) the $\mathrm{C}=\mathrm{C}$ is one carbon further away, so there is no resonance. a $<$ b.