Question

The elements in the Mendeleev’s periodic table were arranged in the increasing order of their atomic masses. But, the sequence was inverted so that two elements with similar properties could be grouped together. Identify those two elements.

• A. Cobalt (Co) and Nickel (Ni)
• B. Potassium (K) and Calcium (Ca)
• C. Lithium (Li) and Sodium (Na)
• D. Beryllium (Be) and Magnesium (Mg)

Answer 1

The correct option is A Cobalt (Co) and Nickel (Ni)

While developing the periodic table, there were a few instances where Mendeleev had to place an element with a slightly higher atomic mass before an element with a slightly lower atomic mass. The sequence was inverted so that elements with similar properties could be grouped together. For example, Cobalt (58.9) appeared before Nickel (58.7).