Which of the following is most stable?

Which of the following species is a radical?

Which of the following compounds gives the same carbocation on ionization?

Identify the correct order of stability of the following carbocations:

Consider the following statements. Of these statements:
$(I) \ CH_3O-CH_2^+$ is more stable than $CH_3-CH_2^+$
$(II) \ Me_2CH^+$ is more stable than $CH_3-CH_2-CH_2^+$
$(III) \ CH_2=CH-CH_2^+$ is more stable than $CH_3-CH_2-CH_2^+$
$(IV) \ CH_2=CH^+$ is more stable than $CH_3-CH_2^+$

Which of the following has maximum stability?