Final answer:
In the alpha decay of Gold-185, the nucleus loses an alpha particle resulting in a decrease of the mass number by 4; therefore, the mass number of the resulting element is 181.
Step-by-step explanation:
To determine the product of the alpha decay of Gold-185, we must remember that in alpha decay, an alpha particle (which is a helium nucleus with 2 protons and 2 neutrons) is emitted from the nucleus. Since both protons and neutrons are conserved in nuclear reactions, the mass number of the gold atom will decrease by 4 units (2 protons + 2 neutrons = 4 nucleons) after the emission of an alpha particle. Therefore, the mass number of the resulting element will be 185 - 4 = 181. The atomic number of gold (79) will also decrease by 2, because two protons are lost in the form of the alpha particle. However, the atomic number is not a concern in the given options, as they only ask for the mass number of the resulting element.
Thus, the correct answer for the mass number of the element formed after the alpha decay of Gold-185 is 181.