$\begin{array}{1 1}(a)\;bonding\; \pi-orbitals\;with \;parallel \;spin \\
(b)\; anti-bonding\; \pi-orbitals\;with\;parallel\;spin \\(c)\; antibonding\; \pi-orbitals\;with\;opposite\;spin \\ (d)\; anti-bonding\; \sigma-orbitals\;with \;parallel \; spin \end{array}$
