Multiple choice

Which of the following elements was incorrectly placed in Mendeleev's periodic table?

  1. Boron

  2. Helium

  3. Aluminium

  4. Hydrogen

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Mendeleev's periodic law states that poperties  of elements are periodic functions of their atomic masses. Therefore the elements are arranged in the increasing order of their atomic masses.  However Mendeleev placed cobalt before nickel eventhough it has a slightly higher mass than nickel.