I imagine beryllium is there because people learn "hydrogen, helium, lithium, beryllium". Argon might be there because people learn all the noble gases together.
besides zinc, the symbols do not really match up with the elements, that must be it. (i was surprised not to see tin accepted either, but immediately thought, ow yea...)
Lead is a commonly known substance, but it is not commonly known that it is an element. On the other hand, people better know elements at the start of the table, and elements with an important namesake.