1. Fill in the blank: In nuclear reactions, the process by which an unstable nucleus emits radiation in order to become stable is called _____. Answer: radioactive decay. Rationale: Radioactive decay is the process by which an unstable nucleus emits radiation in the form of particles or energy in order to achieve a more stable configuration. 2. True or False: Half-life is the time it takes for half of the radioactive nuclei in a sample to decay. Answer: True. Rationale: Half-life is the time it takes for half of the radioactive nuclei in a sample to undergo radioactive decay. 3. Multiple Choice: Which of the following particles is commonly emitted during alpha decay? A. Alpha particle B. Beta particle C. Gamma ray D. Neutron Answer: A. Alpha particle Rationale: Alpha decay involves the emission of an alpha particle, which is composed of two protons and two neutrons. 4. Fill in the blank: The equation E=mc^2, where E is energy, m is mass, and c is the speed of light, is proposed by _____. Answer: Albert Einstein. Rationale: Albert Einstein's famous equation E=mc^2 explains the relationship between energy and mass. 5. True or False: Nuclear reactions can lead to the formation of new elements.