Magnetic moment (spin only) of octahedral complex having $CFSE=-0.8{\Delta }_o$ and surrounded by weak field ligands can be :

The correct option is B A and B
The octahedral complex with $CFSE=-0.8{\Delta }_o$ surrounded by weak field ligands can have one or more unpaired electrons.

The spin only magnetic moment is given by the formula ${\mu }_{eff}=\sqrt{n(n+2)}B.M.$.

For two unpaired electrons, the expression becomes ${\mu }_{eff}=\sqrt{2(2+2)}B.M.=\sqrt{8}B.M.$.

For three unpaired electrons, the expression becomes ${\mu }_{eff}=\sqrt{3(3+2)}B.M.=\sqrt{15}B.M.$.

Thus, both options A and B are correct.