Give one example of a pair of elements that would be placed incorrectly if they were in the order of their relative atomic masses on the periodic table. explain why placing these two elements in the order of their relative atomic masses would not be correct.

Cobalt and nickel
nickel has a lower atomic mass number, but has a higher atomic number or more protons. Elements are arranged by atomic number.

Ir and Pt also

Ifound this on google “these two compounds have a different ionic structure. caesium ion is larger in size when compared to the sodium ion. the charge gets more area to spread out evenly. so caesium chloride has a lower melting point than sodium chloride.” i hope this you for what your looking for