$A$ species having carbon with a sextet of electrons and which can act as an electrophile is called:

Which of the following is the least stable carbon free radical?

Which of the following is the most stable carbanion?

The most stable carbocation from the following is:

In which of the following compounds,the $C-Cl$ bond ionisation shall give the most stable carbonium ion?

The correct stability order for the following species is:
$(I)$ $o-CN-C_6H_4-CH_2^-$
$(II)$ $m-CN-C_6H_4-CH_2^-$
$(III)$ $p-CN-C_6H_4-CH_2^-$
$(IV)$ $C_6H_5-CH_2^-$
(Note: The image shows the structures of these carbanions.)