Why did early scientists use atomic mass and not atomic number?
pls answer

When Dmitri Mendeleev created the Periodic Table of the Elements, he decided against arranging them by their atomic numbers based on his correct assumption that those numbers were not totally accurate. When he first began to arrange the 60 known elements in the 1860s, he knew that new elements would eventually be discovered there are now over 100 known elements and that the atomic weights of the elements known at that time had been calculated incorrectly

i'm assuming that the correct answer is indeed the first one/ "a"..