<p>The most abundant elements by mass in the body of a healthy human adult are:</p>

<p>Oxygen (61.4%); Carbon (22.9%); Hydrogen (10.0%) and Nitrogen (2.6%)</p>

<p>The weight which is 75 kg peson would gain if all&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML" class="wrs_chemistry"><mmultiscripts><mi mathvariant="normal">H</mi><mprescripts/><mrow/><mn>1</mn></mmultiscripts></math>&nbsp;atoms are replaced by&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML" class="wrs_chemistry"><mmultiscripts><mi mathvariant="normal">H</mi><mprescripts/><mrow/><mn>2</mn></mmultiscripts></math>&nbsp;atoms is:</p>