Medical College Admission Test (MCAT) 2026 – 400 Free Practice Questions to Pass the Exam

One mole of a substance is defined as the amount of that substance that contains exactly 6.022 x 10²³ entities, which can be atoms, molecules, ions, or other particles. This number is known as Avogadro's number, and it provides a bridge between the microscopic scale of individual atoms and molecules and the macroscopic scale that we can measure in the laboratory. Therefore, option B correctly encapsulates the concept of a mole, as it focuses on the quantity of particles present in one mole of a substance. This is a fundamental concept in chemistry that allows scientists to count and measure substances in a standardized way, making it easier to perform calculations and predict the behavior of chemical reactions.