The correct response is:
Protons attract the particles, while neutrons do not.
In a nucleus, protons are positively charged and exert an electrostatic attractive force on negatively charged particles, such as electrons or alpha particles, while neutrons are neutral and do not contribute to electrostatic interactions. Therefore, in the case of nuclei with 20 protons and 100 neutrons, the protons can effectively attract the alpha particles. In contrast, when the nuclei have 100 protons and 20 neutrons, the increased positive charge creates a stronger repulsive force among the protons, which can prevent the alpha particles from getting as close to the nucleus.