Answer:
The correct option is D.
Explanation:
Radioactive substances usually emit different types of particles when they are decaying. Such particles include alpha particles, beta particles and gamma ray. When an alpha particle is emitted from an unstable radioactive nucleus such nucleus usually lost an atomic mass that correspond to that of helium atom. Note that an alpha particle is made up of two protons and two neutrons, which result in mass number of 4. Thus, a nucleus that emit an alpha particle will have its mass number (atomic mass) reduce by 4 and atomic number that is reduced by 2.
When an alpha particle is emitted from an unstable nucleus, the atomic mass number of the nucleus Decreases by 4.
These are composite particles that are made up with two protons and neutrons tightly bond together.
These radioactive substances normally give out different particles especially when they are decaying. When the alpha particles are emitted from an unstable system, nucleus usually lose an atomic mass and they correspond to the helium atom. Since the alpha particles are made up of two protons and neutrons, they lost mass number is reduced by 4 and atomic number by 2.
Learn more about Alpha Particles here:
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