Compounds x has the formula c7h15cl; y is c7h15br. x undergoes base-promoted e2 elimination to give a single alkene product z. y likewise reacts under similar conditions to give a single alkene product that is isomeric with z catalytic hydrogenation of z affords 3-ethylpentane. x readily reacts in sn2 fashion with sodium iodide in acetone. y does not undergo a similar sn2 reaction. propose structures for x and y.

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.