Question

What will be the daughter nuclei after 4 alpha decays of ${}_{91}^{231}Pa$?

• A. ${}_{89}^{227}X$
• B. ${}_{83}^{215}X$
• C. ${}_{75}^{215}X$
• D. ${}_{78}^{215}X$

Answer 1

The correct option is B

${}_{83}^{215}X$

An alpha ray is a Helium nuclei with atomic number 2 and mass number 4.
One alpha ray emission reduces the atomic number by 2 and mass number by 4.
So 4 alpha ray emission will totally reduce the atomic number by 8 and mass number by 16.
Now let's check the options and see which one fits.
Mass number will become 231-16 = 215
Atomic number will become 91-8 = 83
${}_{83}^{215}X$