Three long current carrying wires, $P, Q$ and $R$, are placed perpendicular to the plane of a paper. Magnetic force per unit length, on the wire $R$, is

A current carrying loop is placed in a uniform magnetic field, as shown. The torque on the loop is 

Four wires, of equal length, are bent in the form of four loops, $P, Q, R$ and $S$. They are suspended in a uniform magnetic field and same current is passed through them. The maximum torque will act on