A fossil fuel formed deep inside the earth, often found with oil, and sometimes used to heat homes during the cold weather is called . Natural Gas

Petroleum

Petrochemical

Lumber

am i too late?

explanation:

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.