Neutrons are used to induce artificial radioactivity because they

Analyze the question: Artificial radioactivity is produced by bombarding a stable nucleus with a particle so that it becomes unstable. The question asks why neutrons are especially suitable for this.

Explain the concept:

• The nucleus is positively charged because of its protons.
• Any positively charged projectile, such as a proton or an alpha particle, is repelled by the nucleus (Coulomb repulsion). To get close enough, it needs a very high energy, which requires particle accelerators.
• A neutron is electrically neutral, so it feels no electrostatic repulsion from the nucleus. Even slow (thermal) neutrons can penetrate the nucleus and be captured.

Step-by-step solution:

1. Check A, "are energetic": Neutrons don't have to be energetic. Slow neutrons are often more effective at being captured. So A is wrong.
2. Check B, "have no charge": This is the key property. With no charge, there is no repulsion from the nucleus, so neutrons can enter easily. B is correct.
3. Check C, "have no mass": False. A neutron has a mass of about 1 u, almost the same as a proton.
4. Check D, "are ionizing": Neutrons are not directly ionizing precisely because they are uncharged. So D is wrong.

Example: ²⁷₁₃Al + ¹₀n → ²⁸₁₃Al (radioactive). The neutron is simply absorbed.

Answer: B. Neutrons have no charge, so they are not repelled by the positively charged nucleus.

Exam tip: Whenever you see "why neutrons penetrate the nucleus," think "neutral, so no repulsion." Remember: Neutron = Neutral.