In which one of the following pairs the central atoms exhibit $$\mathrm{sp}^2$$ hybridization ?

Relative stability of the contributing structures is :

Correct order of basic strength of Pyrrole , Pyridine and Piperidine is :

For the given compounds, the correct order of increasing $$\mathrm{pK}_{\mathrm{a}}$$ value :

Choose the correct answer from the options given below :