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If there is no change in the atomic number and mass number of a radioactive material, then the particle emitted is-
1. Proton
2. Neutron
3. Electron
4. Photon

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Correct Answer - Option 4 : Photon



  • A photon is a bundle of electromagnetic energy.
  • They have zero mass and rest energy and they have no electric charge.
  • They carry energy and momentum which are dependent on the frequency.
  • It is the basic unit that makes up all light.
  • The photon is sometimes referred to as a "quantum" of electromagnetic energy.

Gamma radiation:

  • These are the electromagnetic radiation that is emitted by an unstable nucleus of an atom during radioactive decay.
  • Electromagnetic radiation can be described in terms of a stream of photons, which are massless particles each travelling in a wave-like pattern and moving at the speed of light. 
  • It consists of the shortest wavelength electromagnetic waves and so imparts the highest photon energy. 


Charge and mass of electron, proton, neutron and photon: 

Emitted Particle Charge Mass
Electron -1 ≈ 0
Proton 1 1
Neutron 0 1
Photon 0 Rest mass zero
  • From the above table, as we can see, Photon contains zero charges and mass.

Hence, if there is no change in the atomic number and mass number of radioactive material, then the emitted particle will be Photon.

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