Question

question 6
when a nucleus emits a beta particle, its atomic number
remains constant, but its mass number changes.
remains constant, and so does its mass number.
changes, but its mass number remains constant.
changes, and so does its mass number.

Explanation:

To solve this, we recall beta decay: a neutron in the nucleus turns into a proton, emitting a beta particle ($\beta^-$). Atomic number (Z) is the number of protons, so Z increases by 1 (changes). Mass number (A) is protons + neutrons. Since a neutron becomes a proton, A (protons + neutrons) remains the same (neutron → proton, so total nucleons don't change). So atomic number changes, mass number is constant.

Answer:

C. changes, but its mass number remains constant.