* Protons: The number of protons defines the element. Technetium (Tc) has an atomic number of 43, meaning it has 43 protons.
* Neutrons: The mass number (99 in this case) represents the total number of protons and neutrons in the nucleus. To find the number of neutrons, subtract the atomic number from the mass number: 99 - 43 = 56 neutrons.
* Electrons: In a neutral atom, the number of electrons is equal to the number of protons. So technetium-99 has 43 electrons.
In summary:
* Protons: 43
* Neutrons: 56
* Electrons: 43
