IGCSE Physics Practice Exam 2025 – All-in-One Study Guide for Exam Success!

When an alpha particle is emitted from an atomic nucleus, the atomic number of the element decreases by 2. An alpha particle consists of 2 protons and 2 neutrons (essentially a helium-4 nucleus). During the emission of an alpha particle, the original nucleus loses these 2 protons, which directly reduces its atomic number. The atomic number determines the element's identity, so a decrease by 2 means the element transforms into a different element that is two places back on the periodic table.

The correct option is supported by understanding that the emission processes, such as alpha decay, change the nucleus's structure and mass. The loss of protons not only affects the atomic number but also alters the overall nucleon count, which leads to other characteristics such as stability and the type of decay the element may undergo next. Therefore, the emission of an alpha particle results in a decrease of 2 in the atomic number of the original element.