When an atom undergoes beta decay and emits a beta particle, what is the change in its atomic mass number?

• A. The atomic mass number decreases by 1.
• B. The atomic mass number increases by 1.
• C. The atomic mass number increases by 2.
• D. The atomic mass number remains unchanged.

Answer: (D)

Verified step by step guidance

1. Understand that beta decay involves the transformation of a neutron into a proton within the nucleus, accompanied by the emission of a beta particle (an electron) and an antineutrino.
2. Recall that the atomic mass number (A) is the total number of protons and neutrons in the nucleus.
3. In beta decay, since a neutron changes into a proton, the total number of nucleons (protons + neutrons) remains the same, so the atomic mass number does not change.
4. Note that while the atomic number (Z) increases by 1 because a neutron becomes a proton, the atomic mass number (A) stays constant.
5. Therefore, the correct conclusion is that the atomic mass number remains unchanged during beta decay.