The first step in the decay chain of 232 90th is an alpha decay. what is the daughter nucleus formed by this first decay?

Answer is: the daughter nucleus formed by this first decay 228/88Ra.

Alpha particle is nucleus of a helium-4 atom, which is made of two protons and two neutrons.

Nuclear reaction: ²³²Th → ²² ⁸Ra + 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.