Density is mass per unit of volume. Which pair of lab instruments would a student use to measure the density of seawater? a caliper and a flask
a stopwatch and a beaker
a balance and a beaker
a meter stick and a temperature probe

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.

i think that is new experiments yield untrustworthy data and should be carefully considered, because you don't know what will happen with the experiments.

that is wrong, its not thymus.