Respiration occurs in the 1 nasal cavity
2 lungs
3 red blood cells
4 cells of the body

cells of the body

Explanation:

Respiration happens in the cells of plants, animals and humans, mainly inside mitochondria, which are located in a cell’s cytoplasm, energy released during respiration is used by plants to make amino acids, and by animals and humans to contract their muscles to let them move. Don't confuse respiration with breathing. Respiration releases energy, while breathing

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.