Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)
(a) mass
(b) speed
(c) velocity
(d) momentum
When a proton moves in the magnetic field, it experiences a force. this force will always be in a direction perpendicular to the direction of motion, so, the proton will always perform the circular motion. therefore, the velocity and momentum can change,
Hence option (c) and (d) are the correct option.