Some kid of 10years and 13 years needed for friends

What is called the "building block" of life?

I’m doing some practice exam questions for biology, and i’m not sure how to do these 3 parts to the question.

Pentane with molecular formula c5h12, exists in three isomeric forms. one shows linear carbon chains, another has one -ch3 groups present on the third carbon atom, and the third has two -ch3 groups present on the second carbon atom. what types of isomers are these? a. geometric isomers b. structural isomers c. halotropic isomers