A short bar magnet of magnetic moment $m= 0.32 \;J/T$. is placed in a uniform magnetic field of $0.15 \;T$. If the bar is free to rotate in the plane of the field, Which orientation would correspond to its unstable equilibrium ? What is the potential energy of the magnet?

Question

$\begin{array}{1 1} -4.8 \times 10^{-2}\;J \\ 4.8 \times 10^{-2}\;J \\ 48 \times 10^{-2}\;J \\ -48 \times 10^{-2}\;J \end{array} $