The correct order of acidity of the following compounds is

The most stable carbocation among the following is:

Which of the following orders correctly depicts the decreasing order of stability of carbanion?

Hyperconjugation involves the overlap of which of the following orbitals?

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 $IV > V > I > II > III$.

Explain why alkyl groups act as electron donors when attached to a $\pi$ system.