Nitrogen has an atomic mass of 14.007 amu. nitrogen has two common isotopes. one has a mass of 14.003 amu and relative abundance of 99.632%.
a) what is the percent abundance of the other isotope?
b) what is the mass of the other isotope?
i know how to find average atomic mass, but my chem teacher hasn't shown is anything like this and it's on our study guide. how do i do this and how can i remember for the test?

6.4 cm (max) - 25 cm (min)

the answer is d.) potassium

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.