Identify the least stable ion amongst the following

${\mathrm{Li}}^{-}=1{\mathrm{s}}^2, 2{\mathrm{s}}^2$ (In it all sub-shells are saturated, so it is stable)

$$\begin{gathered} {\mathrm{Be}}^{-}=1{\mathrm{s}}^2, 2{\mathrm{s}}^2 2{\mathrm{p}}^1 (\mathrm{Very} \mathrm{much} \mathrm{less} \mathrm{stable}) \\ {\mathrm{B}}^{-}=1{\mathrm{s}}^2, 2{\mathrm{s}}^2 2{\mathrm{p}}^2 (\mathrm{Less} \mathrm{stable}) \\ {\mathrm{C}}^{-}=1{\mathrm{s}}^2, 2{\mathrm{s}}^2 2{\mathrm{p}}^3 (\mathrm{Stable} \mathrm{due} \mathrm{to} \mathrm{presence} \mathrm{of} \mathrm{half}-\mathrm{filled} 2\mathrm{p}-\mathrm{sub}-\mathrm{shell}) \end{gathered}$$