Explain contribution of Mendleev for arrangement of elements in his periodic table

Mendeleev arranged the elements in order of increasing relative atomic mass. When he did this he noted that the chemical properties of the elements and their compounds showed a periodic trend. He then arranged the elements by putting those with similar properties below each other into groups.

-- He left gaps for yet to be discovered elements

-- He switched the order of a few elements to keep the groups consistent

-- He was the first scientist to give the periodic law.

the answer would be a

2b2t

explanation:

2b2t