Final answer:
The atomic number of the resulting atom after 232/90 Th emits an alpha particle is 88, corresponding to the element radium (Ra).
Step-by-step explanation:
When the isotope 232/90 Th emits an alpha particle, the atomic number of the resulting atom decreases by 2 due to the loss of the two protons that the alpha particle consists of. Alpha particles are represented by the symbol He, which has an atomic number of 2 and a mass number of 4. Since thorium (Th) has an atomic number of 90, the emission of an alpha particle will result in an atom with an atomic number of 88, which identifies the element as radium (Ra). According to the law of conservation of matter, which applies to nuclear equations, the resulting isotope will also have a mass number reduced by 4, from 232 to 228, giving us the isotope 228/88 Ra.