Which rays are not deflected in an electric or a magnetic field?
A) alpha rays
B) beta rays
C) gamma rays
D) all of the above

Hint : Only charged particles will be deflected in electric or magnetic fields. Alpha rays and beta rays have net charges while gamma rays are high energy electromagnetic waves.

Complete step by step answer:
Whenever a charged particle moves in an electric field, it is deflected by the electric field or magnetic field.
Alpha particles are positively charged as they have two protons and two neutrons. While the neutrons don’t have a charge, the protons have a net positive charge and as a result, alpha particles have a positive charge. Alpha particles can also be thought of as helium nuclei.
Beta particles are negatively charged and have one unit of negative charge. Beta particles are essentially electrons which are emitted due to various radioactive processes.
Gamma radiation is electrically neutral. Gamma rays are high energy electromagnetic waves which do not have a net electrical charge. This means that alpha and beta radiation can be deflected by electric fields, but gamma radiation cannot.
Hence the types of waves that cannot be deflected by an electric field or a magnetic field are gamma rays.
So the correct choice is option (C).

Note:
While the electric field can act on static as well as moving charges, the magnetic field can only exert force on charges that are moving with a non-zero velocity in the magnetic field. So stationary alpha particles and beta particles in a magnetic field will not experience any force. The magnitude of this force is calculated by the Lorentz formula and depends on the orientation of the electric and the magnetic field.