Question

How is the problem regarding the
position of cobalt (59Co) and nickel
(59Ni) in Mendeleev's periodic table
resolved in modern periodic table?​

Answer 1

Answer:

As per Mendeleev's classification, elements are arranged in an increasing order of atomic masses, but cobalt, with a higher atomic mass was placed before nickel. The atomic numbers of cobalt and nickel are 27 and 28 respectively. So, cobalt with a lower atomic number should come before nickel.