Question

Question #ac1e7

Answer 1

C) The number of valence electrons.

Explanation:

Valence electrons are in the highest energy `"s"` and `"p"` sublevels. The number of valence electrons is the same for the elements in the same group. For example, all of the alkali metals in group 1 have 1 valence electron in their highest energy sublevel. We can see this by looking at their electron configurations.

Electron Configurations of Alkali Metals Using Noble Gas Notation
`"Li":` `"[He]2s"^1"`
`"Na":` `"[Ne]3s"^1"`
`"K":` `"[Ar]4s"^1"`
`"Rb":` `"[Kr]5s"^1"`
`"Cs":` `"[Xe]6s"^1"`
`"Fr":` `"[Rn]7s"^1"`

By using the noble gas notation, it is very easy to see that all of the alkali metals have the same number of valence electrons, which is `"ns"^1"`.

The diagram below shows the valence electrons for the main group elements (representative elements) in periods 2 and 3. You can see that the members of each group have the same number of valence electrons.