Answer the following question given this paragraph: Beta decay occurs when an unstable nucleus emits a beta particle and energy. A beta particle is an electron. It has a charge of -1. In nuclear equations, a beta particle is represented by the symbol . The subscript -1 represents the particle's charge, and the superscript 0 shows that the particle has virtually no mass. Nuclei contain only protons and neutrons, so how can a nucleus emit an electron? A neutron first breaks down into a proton and an electron (see Figure below ). Then the electron is emitted from the nucleus, while the proton stays inside the nucleus. The proton increases the atomic number by one, thus changing one element into another. Q: What occurs when an unstable nucleus emits a beta particle and energy? A:

i. nucleus decay. ii. alpha decay. iii. methane decay. iv. beta decay.
The answer is:
iv.