The relative atomic mass of boron 10.2.if the element occurs in two isotopic forms, boron-10 and boron-11 ,what are their geometrical abundances?

Find the abundance of each isotope.

Let y/100 = the abundance of copper-10
and (100 - y)/100 = the abundance of copper-11

10.2 = (y/100 x 10) + [(100 - y)/100 x 11] 
10.2 = 10y/100 + 1100/100 - 11y/100 
1020 = 10y + 1100 - 11y 
-80 = -y 
y = 80

Abundance of boron-10 = 10/100 = 10%

Abundance of boron-11 = 100 - 10 = 90%

nuclear fission produces elements that are heavier than helium.

the elements that are used in nuclear fission and their products are much heavier than helium.