Final answer:
Subtracting one proton and three neutrons from a mercury atom would convert it into gold (Au), since the atomic number would change from 80 (mercury) to 79 (gold).
Step-by-step explanation:
If you could subtract one proton and three neutrons from a mercury atom, you would convert it into gold (Au). On the periodic table, mercury (Hg) has an atomic number of 80 and its most stable isotopes have more than 80 neutrons each. Since the atomic number defines the element, removing one proton would decrease the atomic number to 79, which is the atomic number of gold. Additionally, subtracting three neutrons from one of the most abundant isotopes of mercury, which likely has more than 120 neutrons, would result in an isotope of gold with a slightly lower mass number than the isotopes of mercury from which it was derived.