The atomic number of an element represents the number of protons in the nucleus, while the mass number represents the sum of protons and neutrons. If an isotope has an atomic number equal to its mass number, it means that the number of protons and neutrons is the same, indicating an equal number of protons and neutrons in the nucleus.
This specific isotope is hydrogen-1, also known as protium. Hydrogen-1 has an atomic number of 1 and a mass number of 1, which means it consists of a single proton and no neutrons. It is the most abundant and commonly found isotope of hydrogen.