The electron displacement in a covalent bond of a molecule is produced by which type of effects?

Show the polarisation of the carbon-magnesium bond in the following structure: $CH_3-CH_2-CH_2-CH_2-MgX$.

Given below are two statements:
Statement $I$: On the basis of inductive effect, the order of stability of alkyl carbanions is $CH_3^- > CH_3CH_2^- > (CH_3)_2CH^- > (CH_3)_3C^-$.
Statement $II$: Allyl and benzyl carbanions are more stabilised by inductive effect and not by resonance effect.

The electron displacement effect observed in the given structures is known as

Identify the group that exerts electron withdrawing resonance effect.

With respect to the compounds $I-V$,choose the correct statement$(s)$.
$(A)$ The acidity of compound $I$ is due to delocalization in the conjugate base.
$(B)$ The conjugate base of compound $IV$ is aromatic.
$(C)$ Compound $II$ becomes more acidic,when it has a $-NO_2$ substituent.
$(D)$ The acidity of compounds follows the order $IV > V > I > II > III$.