In which case electron from bonding molecular orbital is removed?

Question

$\begin{array}{1 1}(a)\;O_2\; to \;O_2^+ \\ (b)\; N_2\; to\; N_2^+\\(c)\; NO\; to\; NO^+ \\(d)\; O_2\; to\; O_2^-\end{array}$