Which among the following carbocations is the most reactive?

Which one of the following is most stable?

Consider the following carbocations:
$I. C_6H_5CH_2^+$
$II. CH_2=CH^+$
$III. CH_3-CH^+(CH_3)$
$IV. CH_3-CH_2^+$
$V. HC \equiv C^+$
Arrange the above carbocations in the order of decreasing stability.

Which one of the following is an electrophilic intermediate in the reaction of benzene with $CH_3Cl$ in the presence of anhydrous $AlCl_3$?

The stability of the following carbanions is in the order of:

In which of the following pairs is the $2^{\text{nd}}$ anion more stable than the $1^{\text{st}}$?