FTCE Subject Area Practice Test 2025 – Comprehensive Prep Guide

Atoms that have a different number of neutrons than protons are referred to as isotopes. Isotopes are variations of the same chemical element that contain the same number of protons, which determines the element itself, but differ in their neutron count. This difference in neutrons leads to variations in atomic mass while retaining similar chemical properties.

For example, carbon has several isotopes, including carbon-12 (with 6 protons and 6 neutrons) and carbon-14 (with 6 protons and 8 neutrons). Both are forms of carbon, but their neutron number results in differing physical properties, such as stability and half-life. Isotopes are important in various scientific fields, including chemistry, physics, and medicine, due to their unique characteristics and behavior.

The other choices represent different concepts in science. Ions are atoms or molecules with a net electric charge due to the loss or gain of one or more electrons. Allotropes are different forms of the same element in the same physical state, like graphite and diamond being different allotropes of carbon. Elements refer to pure substances made up of only one type of atom, characterized by its number of protons.