C
which you could easily have discovered after a few seconds with google (or, I suspect, your class text)
What is the weak nuclear force?
a force that attracts objects with mass towards each other
a force that acts on charged particles
a force that governs how elements break down naturally
a force that holds atomic nuclei together
2 answers
The weak nuclear force (or just the weak force, or weak interaction) acts inside of individual nucleons, which means that it is even shorter ranged than the strong force. It is the force that allows protons to turn into neutrons and vice versa through beta decay. This keeps the right balance of protons and neutrons in a nucleus.