Asodium atom that has a mass number of 24

Not sure what the question is, but a standard sodium atom has 11 protons, 11 electrons, and 12 neutrons with an atomic mass of 23. A sodium atom with a mass number of 24 probably has 13 neutrons.

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.