Concept:Radioactive decay emits radiations having different charge, mass, and penetrating power.
A radiation deflected by a magnet must be charged, and one with fairly high penetration is the beta particle.
Explanation:Beta particles are fast-moving electrons emitted from the nucleus during radioactive decay.
They carry a negative charge, so they are deflected by electric and magnetic fields.
They possess momentum because they have both mass and velocity.
Their penetrating power is fairly high compared with alpha particles, though less than gamma rays.
Alpha particles have very low penetrating power and are easily stopped by paper.
Gamma rays are uncharged and therefore are not deflected by a magnet.
X-rays are not typical radiations emitted in ordinary radioactive decay.
Thus beta particles meet all the given conditions.
Answer:B. beta particle