A Level Chemistry OCR Practice Exam

Isotopes are defined as atoms of the same element that have the same number of protons but different numbers of neutrons. This difference in neutron count results in variations in atomic mass among isotopes of a given element, while maintaining the same chemical properties due to the identical number of protons (the atomic number). This characteristic is crucial as it influences various physical properties such as stability and abundance, and it allows for the existence of isotopes within the periodic table. Consequently, option C accurately captures the essence of isotopes, highlighting the importance of neutron count in defining them within the same element. Other options do not describe isotopes correctly. Some mention differences in mass and charges, but isotopes specifically focus on the same element and variations in neutrons alone. Thus, option C is the most precise definition.