The answer is "planet, solar system, galaxy, then universe".
Reason:
A planet would be the smallest because it orbits the sun, then it would be solar system because a solar system is everything that orbits the sun, then it would be galaxy because it contains the solar system, then it would be universe because it contains everything in space: planets, stars, galaxies, comment's, asteroids, etc...
the answer is c. their atomic masses are different clearly because an atom of gold has 79 protons and the atom can be divided multiple times. An atom of silver has an atomic number of 47. 47 electrons. Clearly different. Hope it helps :)
