A particle is projected in a gravity force space where a uniform magnetic field exists. if the trajectory of the particle is a straight line, then the particle

If a neutron is projected in any direction in magnetic field, its path will be a straight line as me magnetic force acts on it. If a charge particle is projected in a uniform magnetic field in a direction parallel to the field, then magnetic force FB→=qV→×B→ acting on the particle will be zero and the trajectory of the particle will be straight line. hence option (4) is correct.