Final answer:
c.electrons. Primary cosmic rays consist mainly of high-speed protons, along with helium, heavier nuclei, electrons, and positrons, with protons making up about 90% of these cosmic particles.
Step-by-step explanation:
Primary cosmic rays are largely composed of very fast-moving particles that come from outside the solar system and reach Earth. The majority of these cosmic rays are high-speed atomic nuclei and electrons.
Almost 90% of cosmic rays are hydrogen nuclei, known as protons, that have been stripped of their accompanying electron. Helium and heavier nuclei make up about 9%, while around 1% of cosmic rays are similar in mass to electrons, with a portion of these being positively charged positrons, a type of antimatter.
These cosmic rays travel at speeds close to 90% of the speed of light, and their origin is often linked to supernova explosions, which can accelerate charged particles to these tremendous velocities.
Primary cosmic rays are composed largely of very fast protons. Almost 90% of the cosmic rays are hydrogen nuclei (protons) stripped of their accompanying electron.
Helium and heavier nuclei constitute about 9% more. About 1% of cosmic rays have masses equal to the mass of the electron, and 10-20% of these carry positive charge rather than the negative charge that characterizes electrons.