The cause of the beta (β) rays emitted from a radioactive nucleus is:

Think it through first, then pick an option.

Answer and explanation

Correct answer: d weak nuclear force

Beta rays, or electrons, leave a radioactive nucleus because of the weak nuclear force.

Why the other options are wrong

a gravitational force: Gravity is the weakest force; it is not what emits beta rays.
b electromagnetic force: The electromagnetic force acts between charges and magnets; the book does not give it as the cause of beta rays.
c strong nuclear force: The strong nuclear force holds protons and neutrons in; it is not the cause of beta emission.