Chemistry - GOC Question with Solution | TestHub

In (a) the N lone pair is pushed through the $\mathrm{C}=\mathrm{C}$ to the $\mathrm{C}=\mathrm{O}$ (push-pull system), so the C-N bond has double-bond character and is short. In (b) the C-N bond is a plain single bond. So a $<$ b.