Which of the following elements were not known when Mendeleev published his periodic table?

Options

A. Lanthanodis
B. Actinoids
C. Noble gases
D. Noble metals

Answer

C

Explanation

Mendeleev's original periodic table was modified from time to time as more elements were discovered with the passage of time. When noble gases were discovered around the year `1900`, a new group called the zero group was added to Mendeleev's original periodic table.
Later on, two groups of `14` elements each called lanthanides and actinides were placed at the bottom of the modified Mendeleev's periodic table.