Describe two reasons why an alpha particle is less penetrating than a beta or gamma particle.

Because of its relatively large mass and charge, an alpha particle produces ions in a very localized area. An alpha particle loses some of its energy each time it produces an ion, finally acquiring two electrons from an atom at the end of its path to become a helium atom. An alpha particle has a short range (several centimeters) in air. 

The answer is c. 320 g

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