Nonrenewable energy source that is least used?

Question

7 letter word

Answer 1

body fat

Answer 2

Coal

I am from India and I know that coal resources of India can last for 1000 years as compared to 50 years for oil.

Coal based technology was developed in Germany during Hitler's regime as ordered by him as he knew that without that he will have oil scarcity and will lose in war. Coal based technology developed in Germany those days has relevance even today.

Next to coal is the nuclear fuel.

Answer 3

mybrain? I think I haven't used it for quite a while.. :)

Answer 4

n-u-c-l-e-a-r