Question

why couldnt mendeleev organize the entire table during his research?
the elements showed no periodic properties.
the atomic mass was unknown at the time.
the atomic number was unknown at the time.
some elements were undiscovered at the time.

Explanation:

Mendeleev created the periodic table based on the known elements at his time. Since some elements were yet - to - be discovered, he couldn't organize the entire modern - day table. Elements did show periodic properties, atomic mass was known (he used it in his organization), atomic number concept came later but its non - knowledge wasn't the main reason for incomplete organization.

Answer:

Some elements were undiscovered at the time.