Answer:it is due to present of water amount in our body. Our body consists 70%of water and 1/3of oxygen and 2/3 of hydrogen.
Explanation: human body consist of 1/3 of oxygen and 2/3 of hydrogen because oxygen contain 16 times more mass than hydrogen atom, hydrogen has only 1 proton so its atomic no. is 1 whereas oxygen has 8 proton and 8 neutrons so its atomic no.is 8 and mass is 16 so overall it takes 16 hydrogen atoms to equal to the mass of 1 oxygen atom.