Define species, population, community, and ecosystem.

A species is a group of organisms that can breed together to produce fertile offspring
populations are all the organisms of one species in a habitat at a given time
a community is the populations of different species in a habitat 
an ecosystem is all the organisms living in a particular area and all the abiotic conditions. 

Ithink 2 is the correct

You use the atomic number to find out how many protons and neutrons there are in the atom. you use the atomic mass to find out how many protons and electrons there are in the atom.