the _ of an element is the average mass of an element naturally occurring atom, or isotopes, taking into account the _ of each isotopes

the atomic mass of an element is the average mass of an element naturally occurring atom, or isotopes, taking into account the percentage of each isotopes

Explanation:

The atomic mass of an element is obtained by obtaining the relative abundances (in percentages) of naturally occurring atoms and the masses of the isotopes. The atomic mass can also be defined as the sum of the protons and the neutrons in the nucleus of an element.

In the periodic table, the atomic mass is indicated below the symbol of each of the elements and is usually in the decimal form.

i think it's c. i'm not sure but i think so.

geosphere and hydrosphere.

this is because the geosphere has to do with geological events, while the hydrosphere controls all water on earth.