Multiple choice

Compounds of which of the following elements were used as a standard reference by Mendeleev to classify elements?

  1. Hydrogen and oxygen

  2. Carbon and hydrogen

  3. Oxygen and carbon

  4. Hydrogen only

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A Correct answer
Explanation

Mendeleev classified the elements according to their increasing atomic masses in horizontal rows in such a way that the elements with similar chemical properties (i.e. elements with similar formulae of oxides and hydrides) fell in the same vertical column. He preferred only oxygen and hydrogen because oxygen and hydrogen form bond with almost all elements.