Answer
Please see the work below.
Work Step by Step
Beryllium molecule ($Be_{2}$) contains 8 electrons.
The molecular orbital configuration of $Be_{2}$ molecule is as follows,
$(σ_{1s})^{2},(σ^{*}_{1s})^{2}, (σ_{2s})^{2},(σ^{*}_{2s})^{2}$
The bond order is 1/2(number of bonding electrons - number of anti bonding electrons).
Hence bond order of $Be_{2}$ is 1/2(4-4)=0.
Bond order zero corresponds to an unstable molecule.
