Recall that the number of protons in an element is defined by its atomic number, which is unique to each element.
Identify the element in question: lithium. Lithium has an atomic number of 3, meaning it has 3 protons.
Understand that the isotope number (in this case, 8 in lithium-8) represents the sum of protons and neutrons in the nucleus, not the number of protons alone.
Therefore, regardless of the isotope number, the number of protons in lithium remains constant at 3.