A force is exerted on a charge carrying particle by a only when the particle moves the field lines. If a charged particle moves parallel to the magnetic field, the force exerted by the magnetic field on the charged particle is.

  force is exerted on a charge carrying particle by a MAGNETIC FIELD only when the particle moves PERPENDICULAR the field lines. If a charged particle moves parallel to the magnetic field, the force exerted by the magnetic field on the charged particle is_ ZERO

Explanation:

This complementation exercise refers to the magnetic force that the formula has

         F = q v x B

where the bold letters indicate vents and the x the vector product. The module of this product is

         F = qv B sin θ

where θ  is the angle between the speed and direction of the magnetic field.

It can be seen that for the force to be different from zero, the angle must not be parallel θ  = 0

        sin 0 = 0

the maximum value is obtained for an angle of θ  = 90º

       sin 90 = 1

Using these concepts we see that the missing words are.

  force is exerted on a charge carrying particle by a MAGNETIC FIELD only when the particle moves PERPENDICULAR the field lines. If a charged particle moves parallel to the magnetic field, the force exerted by the magnetic field on the charged particle is_ ZERO

the answer for apex is the lowest