Which free radical is most stable among the following?

The stability of carbanions follows the order:
$I: CH_3CH_2CH_2\bar{C}H_2$
$II: CH_3\bar{C}HCH_2CH_3$
$III: (CH_3)_3\bar{C}$
$IV: CH_3\bar{C}(Ph)CH_2CH_3$

For the following bond cleavages,use curved-arrows to show the electron flow and classify each as homolysis or heterolysis. Identify the reactive intermediate produced as free radical,carbocation,or carbanion.

Carbocation as an intermediate is likely to be formed in the reaction:

Which of the following is the most stable carbanion?

Which of the following carbocations is the most stable?