For the elements in the "f-block," how is the row number related to the principal energy level for the last orbital notation of their electron configurations?"

See explanation

Explanation:

Given that the row number is the same as the period or energy level(shell) in which the electron is found.

If we designate this row number as "n", we know that the  highest principal energy level for the f orbitals is obtained as (n-2) f.

Thus, we obtain the highest principal energy levels for the "f block" elements by subtracting 2 from  the row number.

c is the answer because when something is left after something evaporates that shows the chemical change.