Medeleleev arranged the known chemical elements in a table according to increasing ...

A) atomic number

b) number of electrons

c) number of protons

d) mass

A - atomic number. Atomic number represents how many protons are in the element, and they are arranged this way in the table in ascending order.

edit - on second thought they weren't technically known as atomic numbers until after he arranged them, so I guess the better answer in this case is d - mass. It's a trick question since today they're considered arranged by atomic number