Two charged particles 1 and 2 with same velocity, enter a region of uniform magnetic field in a direction perpendicular to the field. If the particles have the same mass, then 

Force on charged particle moving in magnetic field is given by

$\overrightarrow{F}=Q\overrightarrow{V}\times \overrightarrow{B}$. This force is the centripetal force. Therefore 1 must carry negative charge and 2 must carry positive charge.

Also trajectories of the particles are circular with radius of curvature $\gamma =\frac{V_m}{Q{B}_i}$. Since $r_1<r_2\left|Q_1\right|>\left|Q_2\right|$.