Atrain is to cars as a molecule of dna is to

Genes

Explanation:

The cars are the part of the train. This means that the genes are the part of the DNA.

The genes are the small components of the DNA. The functional unit of DNA are genes.

These genes are responsible for the characters that is transferred by DNA from one generation to another generation.

It can be said that the genes are the functional unit of DNA as Cars are the functional unit of train.

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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.