Question

When Mendeleev arranged the elements into the periodic table, he found that elements with ____ fell into groups on the table.

the same mass
similar size
similar properties
the same color

Answer 1

You would have better posted this in Chemistry section.
Anyways, in the periodic table, the elements in a particular group(column) are found to have similar properties. This was later found to be because of the presence of the same number of electrons in the outermost shell of each atom of the element.

Answer 2

He founded a great pattern when arranging the element, he founded that the element in a group is similar in property,
Rather he placed all the element, according to there mass,
it defined many things by just a periodic table, you can know mass, property, future element in a group having similar property
Its totally genious work