The gaps on mendeleev's table have never been filled in represented elements not discovered in his time are not filled in because those elements are gases are not filled in because those elements keep changing

Answer. The gaps on Mendeleev's table have never filled because those elements were not  been discovered at that time.

Explanation:

Mendeleev in his periodic table arranged the elements according to their atomic masses. During this process he encountered that there are missing gaps in his periodic table for which he though , that those missing elements belonging to that particular gap were have not been discovered at that time.He was able to calculate atomic masses of those undiscovered elements and on that basis he predicted their chemical properties and position of them in his periodic table. for example : prediction of gallium's atomic mass and its relative position in his periodic table which was not been discovered at that time.

I’d have to say no because without oxygen in the water the fish would all be dead. so if you want to fish for dead fish, pick the ponds with the lowest oxygen concentrations.

The teacher is mostly talking about the distillation of a mixture