A magnet of magnetic moment 50 i^  Am2   is placed along the x-axis in a magnetic field B→=0.5i^+3.0j^T  . The torque acting on the magnet is

τ→=M→×B→ ⇒τ→=50i^×0.5i^+3j^ ⇒τ→=150i^×j^                                ∵i^×i^=0 ⇒τ→=150k^                                                   ∵ i^×j^=k^