Atomic number is same as the protons ...
Soo... the atomic number would be 18
The difference in cardio-respiratory fitness and cardio-respiratory endurance is a very thin line. Cardio endurance the physical fitness of a person is measured.
It is termed as the ability of a person's body to send nutrients and oxygen continuously to all parts of the body when a physical activity (including lungs and heart) is done for a prolonged period of time. While cardio-respiratory fitness can be called as the fitness of the lungs and heart of a person's body.
Remembering the periodic table, Fe is iron and O is oxygen. The elements that combine to create rust are iron and oxygen, with the chemical compound being (Iron)2(Oxygen)3.
You didn't post the whole question. However the answer would be : Mg, according to former questions in this website.
Hope this helps !
Photon
