Final answer:
Hydrogen is the only non-metal on the left side of the staircase on the periodic table and is the correct answer to the question.
Step-by-step explanation:
The element that is the only non-metal on the left side of the staircase on the periodic table is hydrogen (H). Hydrogen is unique as it is in Group 1 but is not considered an alkali metal like the other elements in the group. All other elements mentioned, such as lithium (Li), beryllium (Be), and helium (He), are either metals or noble gases. Lithium, for instance, is an alkali metal, and helium is a noble gas. Therefore, the correct answer to the student's question is A) Hydrogen.