What is the simplest, smallest matter in the universe? per wiki, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms.
what is the simplest, smallest matter in the world.
wiki gives this illustration (img_1) for Elementary particles included in the Standard Model

 A: This depends on how you define and measure "simplicity" and "smallness".
I will suppose that by "simplicity" you mean "has the fewest separable parts". In that case, to the best extent of our knowledge, what you have on that chart are the simplest material objects, in this sense.
"Smallest", however, is more difficult. All the particles there have zero size, so they are all equally "small" and hence, once more, we could say they are equivalent.
If we mean "has the least mass", then that would depend on whether you consider particles like photons which have no mass at all to be a kind of "matter", or whether matter needs mass. If we say matter needs mass, then neutrinos will be the "smallest" - i.e. least massive - matter. They have some mass, but it's very tiny (on the order of $10^{-10}\ \mathrm{yg}$ or less), smaller than every other particle with nonzero mass.
Hence, I'd say the best answer is likely neutrinos. A single neutrino, to be more precise.
A: “Matter” is a somewhat vague term. However, all the atoms and molecules around us and in our bodies are made of just three kinds of elementary particles: up quarks, down quarks, and electrons. These particles are given mass by the Higgs field — not the Higgs boson — and held together by virtual gluons, which bind up and down quarks into protons and neutrons, and by photons, which bind electrons to nuclei to make atoms, and bind atoms to each other to make molecules.
We can create exotic “matter” out of other quarks and the muon and tau particle but it quickly decays.
I personally consider all quarks, plus the electron, muon, and tau, to be the smallest and simplest matter, but this is just my opinion on some vague terminology.
Most physicists don’t think of neutrinos as being matter, even though they are fermions like the other matter particles. This is because they don’t bind to anything, and are so lightweight that they are more like radiation, usually moving near the speed of light.
Almost no physicists consider bosons to be matter. Instead, the vector bosons are “force carriers” and the Higgs boson is an artifact of the symmetry-breaking mechanism that is responsible for the mass of most elementary particles.
Your diagram shows the 17 particles of today’s Standard Model of particle physics. As far as we know, they are point particles and are not made of anything “smaller” or more fundamental. But we could discover otherwise in the future as we explore nature at smaller scales.
