Answer is: mass number of element is 230.
Alpha particle is nucleus of a helium-4 atom,
which is made of two protons and
two neutrons.
²³⁴U → ²³⁰X + 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.
Explanation:
It is known that an alpha particles is basically a helium nucleus and it contains 2 protons and 2 neutrons.
Symbol of an alpha particle is [tex]^{4}_{2}\alpha[/tex] or [tex]^{4}_{2}He[/tex].
Therefore, when [tex]^{234}_{92}U[/tex] undergoes alpha decay then the reaction will be as follows.
[tex]^{234}_{92}U \rightarrow ^{230}_{90}Th + ^{4}_{2}He[/tex]
Hence, the resulting element formed is thorium.
Therefore, we can conclude that atomic number of the resulting element is 90.
