Question

the chemical formula for the oxygen that we breathe in is o₂. why is o₂ considered an element? o it is naturally occurring. o it is made of only one substance from the periodic table. o it is man - made. o it cannot be broken down into smaller subunits.

Explanation:

An element is a pure substance made up of only one - type of atom and cannot be broken down into simpler substances by chemical means. Oxygen ($O_2$) is made of only oxygen atoms (from the periodic table), and it cannot be broken down into smaller substances by chemical reactions under normal conditions. It is naturally occurring in the atmosphere and is essential for respiration. It is not man - made in the sense that it exists in nature without human synthesis in large quantities. The key characteristic that defines it as an element is that it cannot be broken down into smaller sub - units by chemical means.

Answer:

It cannot be broken down into smaller subunits.