If the thorium-232 isotope emits an alpha particle, what would be the atomic number of the resulting atom?

Answer is: atomic number of resulting atom is 88.
Alpha particle is nucleus of a helium-4 atom, which is made of two protons and two neutrons.
Nuclear reaction: ²³²Th → ²²⁸Ra + α (alpha particle).

Alpha decay is radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and transforms into an atom with an atomic number that is reduced by two and mass number that is reduced by four.

the answer would be a