A pure substance that cannot be broken down into simpler substances by ordinary chemical or physical techniques.  

Which element is likely to be chemically unreactive?​

The smallest unit that retains the chemical and physical properties of an element is a(n) ____.​

The substance O2 is considered to be ____.​

Isotopes of the same element differ from each other in the number of ____.​

All the populations of different organisms that live in the same place form a(n) ____.​

The science of ____ explains the origin and persistence of life, and studies the changes in living things.​

Match the terms to the correct information. 

Compounds that are usually small and simple like carbon dioxide are 

Match the terms to image below.