Assertion (A)When proton and a neutron enter into a transverse magnetic field with equal speeds, then they trace a circular paths of equal radii. Reason (R) In a transverse magnetic field the period of revolution of a charged particle in a circular path is directly proportional to the mass of the particle.

• A

  Both \((\mathrm{A})\) and \((\mathrm{R})\) are correct and \((\mathrm{R})\) is the correct explanation of \((A)\).
• B

  Both \((A)\) and \((R)\) are correct but \((R)\) is not the correct explanation of \((A)\).
• C

  (A) is correct but (R) is not correct.
• Correct answer
  D

  (A) is not correct but (R) is correct.

Hence, the correct answer is option: 'D'.