The functional group that shows negative resonance effect ($-R$ effect) is:

The delocalization of $\sigma$ electrons of $C-H$ bond of an alkyl group with the $\pi$ electrons of benzene is observed in

In which of the following molecules do all the effects,namely inductive,mesomeric,and hyperconjugation,operate?

Which of the following molecule$(s)$ has/have delocalised lone pair$(s)$ of electrons?

Which of the following orders of rotation barrier about the $C=C$ bond,as indicated in the structures below,is correct?
$(I)$ $CH_2=CH_2$
$(II)$ $CH_3O-CH=CH_2$
$(III)$ $CH_3O-CH=CH-COOEt$

Which of the following represents the polarization of electrons in acrolein?