Explanation:
Carbon has four electrons in its outer most orbit and it can share four more electrons from other atom to complete its valency while oxygen has 6 electrons in its outermost orbit and it can either charge the electron or gain two electrons from other atom.
Therefore in 
, the carbon atom shares its two electrons with two electrons of each oxygen atom and forms double bond with it. Thus, total pairs of electron to be shared by the atom of the molecule is two.
Answer:
When ATP molecules are used to fuel movement.
Hopes this helps :))
Basically when doing exercise your body needs way more oxigen because it is using it up faster to be able to do the exercise. While also increasing the breathing rate, the heart rate also goes up because the body needs to pump more blood as the muscles are moving a lot more.
