Question

Find pairs of elements who are out of order with respect to their atomic masses.

The pairs of elements which are out of sequence are:
Te and I
Sg and Bh
Tl and Pb
U and Np
Pu and Am
Th and Pa
Co and Ni
N and O
Tb and Dy
Ar and K
Lr and Rf
Rf and Db

Answer 1

Mendeleev listed elements out of order of their atomic masses to group them with similar properties.

Step-by-step explanation:

Mendeleev had to list some elements out of the order of their atomic masses to group them with other elements that had similar properties. In the figure above, atomic mass increases from top to bottom of vertical columns, with successive columns going left to right. One of Mendeleev's insights is illustrated by the elements tellurium (Te) and iodine (I). Mendeleev reversed the order because he knew that the properties of iodine were much more similar to those of fluorine (F), chlorine (C1), and bromine (Br) than they were to oxygen (O), sulfur (S), and selenium (Se).