The largest deflection of alpha particles will occur when they are influenced most strongly by the field they are passing through. Alpha particles are positively charged, and their deflection is influenced by both their own kinetic energy and the mass and charge of the particles in the field.
To maximize deflection:
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Lower Energy: Higher mass particles in the field will produce a stronger electric or magnetic force on a charged particle, depending on the context. However, lower-energy alpha particles will have a slower velocity, which makes them more susceptible to deflection by interactions with the particles in the field.
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Low Mass-Number Particles: The field of lower mass-number-particles will likely result in a less significant attractive or repulsive force than higher mass-number particles. However, since they are less massive, they can create stronger interactions due to being less hindered by inertia.
Considering these points, the best option for the largest deflection is:
low-energy alpha particles passing through a field of low mass-number-particles.
This combination allows for a greater interaction time and force on the alpha particles, leading to greater deflection.