The smallest parts of these that retain their original properties are called

element , atom

Explanation:

An atom is the smallest part of all the elements found on this planet. An atom is the basic unit just like a cell is the basic unit of life. As a cell has all the original properties of life , an atom also has all the original properties of element.

For example - A single atom of iron will show magnetic properties just like an an iron rod.

Like wise all all chemical properties of an atom are exactly similar to its element.

explanation:

on disadvantage of hydroelectric power is the cost. another disadvantage of using hydroelectric power is finding a water source powerful enough to harvest hydroelectric power.

not sure if this what   you'r looking for would be percent composition