According to the Standard Model of elementary particles, which of the following is NOT a composite object?
E. Alpha particle
Muon is a lepton. Leptons, along with quarks, are considered the fundamental particles.
Pi-Meson consists of a quark and its antiparticle. (Contribution to this part of the solution is due to user danty.) Moreover, a pi-meson is a hadron. Hadrons interact with the strong-force, and all of them are composed of combinations of quarks. (The fundamental particles are classified as quarks and leptons.)
A neutron is made up of 3 quarks.
A deuteron consists of a proton and a neutron. (tritium is two neutrons and a proton, while regular Hydrogen is just an electron and proton).
An alpha particle consists of electrons and protons and neutrons.