Which one of the following is most stable?

Which of the following is the most stable carbocation?

Arrange the following carbocations in increasing order of stability:

In the following carbocation,the $H$ or $CH_3$ group that is most likely to migrate to the positively charged carbon is:

Rank the following radicals in order of increasing stability (least $ < < < $ most).

Arrange the following carbanions in the order of their stability:
$i$. $RC \equiv C^{\ominus}$
$ii$. $C_6H_5^{\ominus}$
$iii$. $R_2C = CH^{\ominus}$
$iv$. $R_3C - CH_2^{\ominus}$