Elements in the same group have simimlar chemical properties due to their identical valence electron shells. Since it is mainly the valence shell involved in chemical reactions, chemical properties tend to depend heavily on valence shell electron configuration. That is why the elements in choice 3) have the most similar chemical properties.
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 :)
