A particular element exists in two stable isotopic forms. One isotope has a mass of 62.9296 amu (69.17% abundance). The other isotope has a mass of 64.9278 amu. Calculate the average mass of the element and determine its identity.

answer is: nuclear fusion produces elements that are heavier than helium.

nuclei combine to form a heavier nucleus, releasing energy.  

for example, fusion of hydrogen atoms at the sun.  

this fusion nuclear reaction is in the inner core of the sun and hydrogen (atomic number 1) is conveted into helium (atomic number 2).  

the inner core is the central region of the sun and all solar energy is produced in the core by nuclear fusion.