Arrange the following carbocations in decreasing order of stability:
$I: CH_3-CH_2^+$
$II: (CH_3)_2CH^+$
$III: Ph-CH_2^+$

Write structures of various carbocations that can be obtained from $2-$methylbutane. Arrange these carbocations in order of increasing stability.

Using curved-arrow notation,show the formation of reactive intermediates when the following covalent bonds undergo heterolytic cleavage:
$(a)$ $CH_{3}-SCH_{3}$
$(b)$ $CH_{3}-CN$
$(c)$ $CH_{3}-Cu$

The increasing order of basicity for the following intermediates is (from weak to strong):
$(i)$ $(CH_3)_3C^{-}$
$(ii)$ $H_2C=CH-CH_2^{-}$
$(iii)$ $HC \equiv C^{-}$
$(iv)$ $CH_3^{-}$
$(v)$ $CN^{-}$

Which carbocation is the least stable?

Explain why $((CH_3)_3C)^+$ is more stable than $(CH_3CH_2)^+$ and $(CH_3)^+$ is the least stable carbocation.