Question

what happens to an atom when it emits a beta particle?
the atomic number decreases by one and the atomic mass remains constant.
the atomic number increases by one while the atomic mass remains constant.
the atomic number decreases by four and the atomic mass decreases by two.
the atomic number and the atomic mass remain constant.
the atomic number decreases by two and the atomic mass decreases by four.

Explanation:

In beta decay, a neutron in the nucleus converts to a proton, emitting a beta particle (electron) and an antineutrino. Since a neutron (no charge) becomes a proton (positive charge), the atomic number (number of protons) increases by 1. The mass number (sum of protons and neutrons) remains constant because a neutron (mass ~1) is replaced by a proton (mass ~1). So we analyze each option:

• First option: Atomic number decreasing is incorrect for beta decay.
• Second option: Matches the beta decay process (atomic number +1, mass constant).
• Third option: Describes alpha decay (atomic number -2, mass -4).
• Fourth option: Incorrect, as beta decay changes atomic number.
• Fifth option: Also alpha decay description.

Answer:

B. The atomic number increases by one while the atomic mass remains constant.