少少問題 10 分

particle = very small thing, but a very general terms, a name only! ~
atom contains protons,neutrons and electrons.
protons, neutrons and electrons can consider as particles.
however, for example, alpha particle = 4He. This is particle as well~

So, there is not very strict definition of particle.... just consider as a general small stuff is ok.

molecule... well, 2 or more atoms form a molecule, e.g. H-Cl, O2, etc. these are molecule. Can you say H2 is particle? you may say yes, or you may say no,depends on your definition of "small"... so in research we seldom use relate particle with molecule.

monomer is not atom. monomer must be a molecule.
linking monomer together to a certain extent (i.e. large enough), you will get polymer. consider 2 monomer link together, you will get dimer, but this is not a polymer as the extent is not large enough.
Polymer is a kind of molecule, or specifically, marcomolecule.

mass .... is the base quantity in the system, which is a relative term.
in chemistry, we have relative atomic mass, mass number, etc. but no "mass".
the terms , in relative to gravity, is weight.