Three ions H+,He+ and O+2 having same kinetic energy pass through a region in which there width is a uniform magnetic field perpendicular to their velocity then,

r=mVBq=2m(KE)Bq rH+=2mP(KE)Be                                 mp is mass of proton rHe+=2 (4mp)(KE)Be=22mp(KE)Be rO+2=2 (16mp)(KE)B(2e)=22mp(KE)Be  We can see that, rHe+=rO+2  , hence they will be deflected equally and  the deflection is inversely proportional radius, H+ deflects most .