When a charged particle is acted on only by a magnetic force, its:

Magnetic force acting on a charge $q$ travelling with velocity $v$ is given by $\vec{F}=q(\vec{v}\times \vec{B})$

Since the force is perpendicular to the velocity, work done by force on the object is always zero. 

Hence the total energy of the charged particle does not change.

Hence correct answer is option D.