Final answer:
The two elements on the periodic table with one valence electron, going right to left, are hydrogen (H) and helium (He), although helium is a noble gas and not typically considered alongside elements with a single valence electron. The element lithium (Li) would be a more suitable example following this periodic trend.
Step-by-step explanation:
The question at hand pertains to identifying elements with one valence electron on the periodic table when traversing right to left. Given the symbols (H, D, A, B, G, C, F, AND E), which seem to be placeholders rather than actual element symbols, the key is to understand the periodic trends of valence electrons.
Looking at the periodic table, hydrogen (H) is the first element and has one valence electron. The next element going right to left that has one valence electron is helium (He), represented by D. However, helium is an exception since it's a noble gas with a full valence shell of two electrons. The question accurately answered, would be Li (lithium) located in the alkali metals or first group, has one valence electron.