What happens during an alpha decay?

Alpha decay is a type of radioactive disintegration in which unstable atomic nucleus releases a helium nucleus or alpha particle and transform into a different element. The new element formed will be reduced by four and the atomic number will be reduced by two.

Example of alpha decay is: Uranium 238 transform into Thorium 234 with the emission of an alpha particle.

it's filtration, but this is an assumption so my apologies if i got this

it's c. elements are placed in rows based on how may valencies electrons have.