Final answer:
The resulting isotope formed after argon-40 reacts with a proton is potassium-40. This is determined by applying the conservation of matter to ensure the balance of atomic and mass numbers.
Step-by-step explanation:
To find the isotope produced from the reaction of argon-40 with a proton, we must use the law of conservation of matter, which tells us that both protons and neutrons are conserved in a nuclear reaction. Therefore, the atomic and mass numbers must be balanced on both sides of the equation. In the given reaction the balanced nuclear equation is 4018Ar + 11H = 4019K + 10n. The resulting isotope formed in this nuclear reaction is potassium-40 (4019K), as both the atomic and mass numbers on both sides of the equation are balanced.