When a charged particle moves perpendicularly to a uniform magnetic field, what best describes its trajectory

A circle.

Explanation:

When a charged particle moves perpendicularly to a uniform magnetic field, what best describes its trajectory is a circle.

This ultimately implies that, a charged particle moving perpendicularly to a uniform magnetic field would undergo or experience a uniform circular motion and this simply, describes its trajectory.

Additionally, the frequency would be directly proportional to the mass of the charged particle.

a.metals can become magnetic if they have many spinning electrons that create magnetic fields.d.only some metals are attracted by magnets; these metals are called ferromagnetic.

d.wrapping an insulated wire around a metal with ferromagnetic properties and applying an electric current.