Assume that a magnetic field exists and its direction is known. then assume that a charged particle moves in a specific direction through that field with velocity (v). which rule do you use to determine the direction of force on that particle?
a. first right-hand rule
b. second right-hand rule
c. third right-hand rule
d. fourth right-hand rule

 The first right-hand rule determines the directions of magnetic force, conventional current and the magnetic field.  Given any two of theses, the third can be found. 
The second Right-Hand Rule determines the direction of the magnetic field around a current-carrying wire and vice-versa 
So, assuming that a magnetic field exists and its direction is known and assuming that a charged particle moves in a specific direction through that field with velocity (v(, to determine the direction of force on the particle we should use the second right-hand rule.