Given the task definition, example input & output, solve the new input case.
Given a scientific passage and an answer, generate a question for the given answer.
Example: Passage: A frameshift mutation is a deletion or insertion of one or more nucleotides that changes the reading frame of the base sequence. Deletions remove nucleotides, and insertions add nucleotides. Consider the following sequence of bases in RNA:. Answer: nucleotides.
Output: A frameshift mutation is a deletion or insertion of one or more of what that changes the reading frame of the base sequence?
The science passage defines frame mutation and the main compoment here is nucleotides. Hence the generated question is apt.

New input case for you: Passage: In the modern periodic table, elements are organized by atomic number. The atomic number is the number of protons in an atom of an element. This number is unique for each element, so it seems like an obvious way to organize the elements. (Mendeleev used atomic mass instead of atomic number because protons had not yet been discovered when he made his table. ) In the modern table, atomic number increases from left to right across each period. It also increases from top to bottom within each group. How is this like Mendeleev's table?. Answer: number of protons
Output:
What is the atomic number?