How may `alpha-` and `beta-` particles will be emitted when `._(90)Th^(232)` changes into `._(82)Pb^(208)`?

Explanation

The given transformation is
`""_(90)Th^(232) to ""_(82)Pb^(208)`
`therefore` Decrease in mass number = 232 - 208 = 24
Number of `alpha`-particles emitted
`=("Total decrease in mass number")/("Mass of one" alpha "particles")`
`24/4 =6`
Expected decrease in atomic number due to emmission of 6 `alpha`-particles = `6 xx 2 =12`
Expected atomic number of nucleus formed = 90-12 = 78
Actual atomic number of the nucleus formed = 82
`therefore` Difference in atomic number = 82 - 78 =4
`rArr` Number of `beta^(-)` particles emitted =4